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 $238.26   8.576%   $258.6932   $258.69   $258.70   $258.70  
  Purchase #2 $13.44   6.592%   $14.326   $14.33   $14.35   $14.30  
  Purchase #3 $62.28   8.734%   $67.7195   $67.72   $67.70   $67.70  
  Purchase #4 $139.28   10.833%   $154.3682   $154.37   $154.35   $154.40  
  Purchase #5 $107.99   10.501%   $119.33   $119.33   $119.35   $119.30  
  Purchase #6 $89.47   11.380%   $99.6517   $99.65   $99.65   $99.70  
  Purchase #7 $199.77   8.636%   $217.0221   $217.02   $217.00   $217.00  
  7 purchase totals = $850.49       $931.1107   $931.11   $931.10   $931.10