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 $115.69   8.872%   $125.954   $125.95   $125.95   $126.00  
  Purchase #2 $31.33   5.554%   $33.0701   $33.07   $33.05   $33.10  
  Purchase #3 $136.74   11.109%   $151.9304   $151.93   $151.95   $151.90  
  Purchase #4 $132.90   5.455%   $140.1497   $140.15   $140.15   $140.10  
  Purchase #5 $200.79   4.813%   $210.454   $210.45   $210.45   $210.50  
  Purchase #6 $102.34   4.548%   $106.9944   $106.99   $107.00   $107.00  
  Purchase #7 $64.32   13.126%   $72.7626   $72.76   $72.75   $72.80  
  7 purchase totals = $784.11       $841.3152   $841.30   $841.30   $841.40