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 $218.80   8.512%   $237.4243   $237.42   $237.40   $237.40  
  Purchase #2 $86.87   12.468%   $97.701   $97.70   $97.70   $97.70  
  Purchase #3 $42.91   8.313%   $46.4771   $46.48   $46.50   $46.50  
  Purchase #4 $199.46   3.447%   $206.3354   $206.34   $206.35   $206.30  
  Purchase #5 $97.98   6.715%   $104.5594   $104.56   $104.55   $104.60  
  Purchase #6 $84.29   8.591%   $91.5314   $91.53   $91.55   $91.50  
  Purchase #7 $11.73   5.551%   $12.3811   $12.38   $12.40   $12.40  
  7 purchase totals = $742.04       $796.4097   $796.41   $796.45   $796.40