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 $84.95   12.251%   $95.3572   $95.36   $95.35   $95.40  
  Purchase #2 $144.56   12.148%   $162.1211   $162.12   $162.10   $162.10  
  Purchase #3 $119.37   5.326%   $125.7276   $125.73   $125.75   $125.70  
  Purchase #4 $91.27   6.451%   $97.1578   $97.16   $97.15   $97.20  
  Purchase #5 $40.96   7.469%   $44.0193   $44.02   $44.00   $44.00  
  Purchase #6 $23.93   13.770%   $27.2252   $27.23   $27.25   $27.20  
  Purchase #7 $144.69   10.423%   $159.771   $159.77   $159.75   $159.80  
  7 purchase totals = $649.73       $711.3792   $711.39   $711.35   $711.40