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 $57.74   10.607%   $63.8645   $63.86   $63.85   $63.90  
  Purchase #2 $238.76   3.747%   $247.7063   $247.71   $247.70   $247.70  
  Purchase #3 $147.42   12.623%   $166.0288   $166.03   $166.05   $166.00  
  Purchase #4 $216.30   8.785%   $235.302   $235.30   $235.30   $235.30  
  Purchase #5 $87.35   10.133%   $96.2012   $96.20   $96.20   $96.20  
  Purchase #6 $167.64   7.367%   $179.99   $179.99   $180.00   $180.00  
  Purchase #7 $111.71   6.350%   $118.8036   $118.80   $118.80   $118.80  
  7 purchase totals = $1,026.92       $1,107.8964   $1,107.89   $1,107.90   $1,107.90