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 $236.53   8.824%   $257.4014   $257.40   $257.40   $257.40  
  Purchase #2 $206.86   7.745%   $222.8813   $222.88   $222.90   $222.90  
  Purchase #3 $68.99   9.835%   $75.7752   $75.78   $75.80   $75.80  
  Purchase #4 $115.83   8.421%   $125.584   $125.58   $125.60   $125.60  
  Purchase #5 $130.82   6.389%   $139.1781   $139.18   $139.20   $139.20  
  Purchase #6 $36.39   4.449%   $38.009   $38.01   $38.00   $38.00  
  Purchase #7 $119.59   5.466%   $126.1268   $126.13   $126.15   $126.10  
  7 purchase totals = $915.01       $984.9558   $984.96   $985.05   $985.00