Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.72   12.711%   $76.3279   $76.33   $76.35   $76.30  
  Purchase #2 $153.35   9.182%   $167.4306   $167.43   $167.45   $167.40  
  Purchase #3 $202.80   11.465%   $226.051   $226.05   $226.05   $226.10  
  Purchase #4 $188.54   12.348%   $211.8209   $211.82   $211.80   $211.80  
  Purchase #5 $15.67   12.522%   $17.6322   $17.63   $17.65   $17.60  
  Purchase #6 $183.92   4.595%   $192.3711   $192.37   $192.35   $192.40  
  Purchase #7 $154.97   5.163%   $162.9711   $162.97   $162.95   $163.00  
  7 purchase totals = $966.97       $1,054.6048   $1,054.60   $1,054.60   $1,054.60