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 $66.82   10.709%   $73.9758   $73.98   $74.00   $74.00  
  Purchase #2 $21.93   7.863%   $23.6544   $23.65   $23.65   $23.70  
  Purchase #3 $167.73   11.647%   $187.2655   $187.27   $187.25   $187.30  
  Purchase #4 $178.54   12.163%   $200.2558   $200.26   $200.25   $200.30  
  Purchase #5 $60.66   7.338%   $65.1112   $65.11   $65.10   $65.10  
  Purchase #6 $160.55   9.388%   $175.6224   $175.62   $175.60   $175.60  
  Purchase #7 $29.79   6.358%   $31.684   $31.68   $31.70   $31.70  
  7 purchase totals = $686.02       $757.5691   $757.57   $757.55   $757.70