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 $72.71   4.664%   $76.1012   $76.10   $76.10   $76.10  
  Purchase #2 $207.67   4.741%   $217.5156   $217.52   $217.50   $217.50  
  Purchase #3 $154.76   11.119%   $171.9678   $171.97   $171.95   $172.00  
  Purchase #4 $27.94   11.814%   $31.2408   $31.24   $31.25   $31.20  
  Purchase #5 $83.87   3.111%   $86.4792   $86.48   $86.50   $86.50  
  Purchase #6 $36.88   9.407%   $40.3493   $40.35   $40.35   $40.30  
  Purchase #7 $177.79   3.745%   $184.4482   $184.45   $184.45   $184.40  
  7 purchase totals = $761.62       $808.1021   $808.11   $808.10   $808.00