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 $168.94   9.193%   $184.4707   $184.47   $184.45   $184.50  
  Purchase #2 $245.52   5.862%   $259.9124   $259.91   $259.90   $259.90  
  Purchase #3 $235.67   3.438%   $243.7723   $243.77   $243.75   $243.80  
  Purchase #4 $195.94   5.621%   $206.9538   $206.95   $206.95   $207.00  
  Purchase #5 $101.78   10.388%   $112.3529   $112.35   $112.35   $112.40  
  Purchase #6 $249.76   11.684%   $278.942   $278.94   $278.95   $278.90  
  Purchase #7 $247.41   3.267%   $255.4929   $255.49   $255.50   $255.50  
  7 purchase totals = $1,445.02       $1,541.8970   $1,541.88   $1,541.85   $1,542.00