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 $71.91   6.138%   $76.3238   $76.32   $76.30   $76.30  
  Purchase #2 $208.77   11.219%   $232.1919   $232.19   $232.20   $232.20  
  Purchase #3 $59.58   13.451%   $67.5941   $67.59   $67.60   $67.60  
  Purchase #4 $208.31   13.470%   $236.3694   $236.37   $236.35   $236.40  
  Purchase #5 $167.26   13.464%   $189.7799   $189.78   $189.80   $189.80  
  Purchase #6 $18.53   11.853%   $20.7264   $20.73   $20.75   $20.70  
  Purchase #7 $12.93   8.134%   $13.9817   $13.98   $14.00   $14.00  
  7 purchase totals = $747.29       $836.9672   $836.96   $837.00   $837.00