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 $112.56   12.324%   $126.4319   $126.43   $126.45   $126.40  
  Purchase #2 $150.75   7.243%   $161.6688   $161.67   $161.65   $161.70  
  Purchase #3 $240.87   10.519%   $266.2071   $266.21   $266.20   $266.20  
  Purchase #4 $177.26   4.787%   $185.7454   $185.75   $185.75   $185.70  
  Purchase #5 $224.27   3.572%   $232.2809   $232.28   $232.30   $232.30  
  Purchase #6 $232.77   9.829%   $255.649   $255.65   $255.65   $255.60  
  Purchase #7 $44.76   8.365%   $48.5042   $48.50   $48.50   $48.50  
  7 purchase totals = $1,183.24       $1,276.4873   $1,276.49   $1,276.50   $1,276.40