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 $40.28   9.621%   $44.1553   $44.16   $44.15   $44.20  
  Purchase #2 $182.46   6.334%   $194.017   $194.02   $194.00   $194.00  
  Purchase #3 $46.53   11.262%   $51.7702   $51.77   $51.75   $51.80  
  Purchase #4 $229.73   5.228%   $241.7403   $241.74   $241.75   $241.70  
  Purchase #5 $124.71   13.356%   $141.3663   $141.37   $141.35   $141.40  
  Purchase #6 $64.58   13.482%   $73.2867   $73.29   $73.30   $73.30  
  Purchase #7 $22.41   10.738%   $24.8164   $24.82   $24.80   $24.80  
  7 purchase totals = $710.70       $771.1522   $771.17   $771.10   $771.20