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 $162.54   12.650%   $183.1013   $183.10   $183.10   $183.10  
  Purchase #2 $199.25   11.776%   $222.7137   $222.71   $222.70   $222.70  
  Purchase #3 $247.25   11.109%   $274.717   $274.72   $274.70   $274.70  
  Purchase #4 $171.47   9.317%   $187.4459   $187.45   $187.45   $187.40  
  Purchase #5 $145.53   11.287%   $161.956   $161.96   $161.95   $162.00  
  Purchase #6 $125.99   12.105%   $141.2411   $141.24   $141.25   $141.20  
  Purchase #7 $29.82   10.579%   $32.9747   $32.97   $32.95   $33.00  
  7 purchase totals = $1,081.85       $1,204.1497   $1,204.15   $1,204.10   $1,204.10