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 $52.65   11.291%   $58.5947   $58.59   $58.60   $58.60  
  Purchase #2 $158.70   9.176%   $173.2623   $173.26   $173.25   $173.30  
  Purchase #3 $244.69   6.847%   $261.4439   $261.44   $261.45   $261.40  
  Purchase #4 $181.66   12.374%   $204.1386   $204.14   $204.15   $204.10  
  Purchase #5 $66.86   5.673%   $70.653   $70.65   $70.65   $70.70  
  Purchase #6 $41.91   8.181%   $45.3387   $45.34   $45.35   $45.30  
  Purchase #7 $195.65   6.848%   $209.0481   $209.05   $209.05   $209.00  
  7 purchase totals = $942.12       $1,022.4793   $1,022.47   $1,022.50   $1,022.40