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 $92.38   3.798%   $95.8886   $95.89   $95.90   $95.90  
  Purchase #2 $118.95   5.243%   $125.1865   $125.19   $125.20   $125.20  
  Purchase #3 $200.99   8.650%   $218.3756   $218.38   $218.40   $218.40  
  Purchase #4 $78.51   3.248%   $81.06   $81.06   $81.05   $81.10  
  Purchase #5 $183.39   5.106%   $192.7539   $192.75   $192.75   $192.80  
  Purchase #6 $41.70   5.624%   $44.0452   $44.05   $44.05   $44.00  
  Purchase #7 $22.63   9.418%   $24.7613   $24.76   $24.75   $24.80  
  7 purchase totals = $738.55       $782.0711   $782.08   $782.10   $782.20