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 $106.85   10.838%   $118.4304   $118.43   $118.45   $118.40  
  Purchase #2 $75.54   10.644%   $83.5805   $83.58   $83.60   $83.60  
  Purchase #3 $232.66   12.503%   $261.7495   $261.75   $261.75   $261.70  
  Purchase #4 $185.49   5.399%   $195.5046   $195.50   $195.50   $195.50  
  Purchase #5 $94.47   3.679%   $97.9456   $97.95   $97.95   $97.90  
  Purchase #6 $209.50   11.289%   $233.1505   $233.15   $233.15   $233.20  
  Purchase #7 $248.26   3.339%   $256.5494   $256.55   $256.55   $256.50  
  7 purchase totals = $1,152.77       $1,246.9105   $1,246.91   $1,246.95   $1,246.80