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 $49.31   13.433%   $55.9338   $55.93   $55.95   $55.90  
  Purchase #2 $123.54   13.237%   $139.893   $139.89   $139.90   $139.90  
  Purchase #3 $127.86   10.600%   $141.4132   $141.41   $141.40   $141.40  
  Purchase #4 $63.58   7.784%   $68.5291   $68.53   $68.55   $68.50  
  Purchase #5 $66.59   9.613%   $72.9913   $72.99   $73.00   $73.00  
  Purchase #6 $191.68   12.189%   $215.0439   $215.04   $215.05   $215.00  
  Purchase #7 $120.60   3.742%   $125.1129   $125.11   $125.10   $125.10  
  7 purchase totals = $743.16       $818.9172   $818.90   $818.95   $818.80