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 $194.66   8.198%   $210.6182   $210.62   $210.60   $210.60  
  Purchase #2 $47.43   11.683%   $52.9712   $52.97   $52.95   $53.00  
  Purchase #3 $60.50   4.420%   $63.1741   $63.17   $63.15   $63.20  
  Purchase #4 $214.66   3.519%   $222.2139   $222.21   $222.20   $222.20  
  Purchase #5 $32.98   4.421%   $34.438   $34.44   $34.45   $34.40  
  Purchase #6 $231.40   11.460%   $257.9184   $257.92   $257.90   $257.90  
  Purchase #7 $182.34   8.105%   $197.1187   $197.12   $197.10   $197.10  
  7 purchase totals = $963.97       $1,038.4525   $1,038.45   $1,038.35   $1,038.40