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 $112.99   11.867%   $126.3985   $126.40   $126.40   $126.40  
  Purchase #2 $221.34   5.811%   $234.2021   $234.20   $234.20   $234.20  
  Purchase #3 $154.76   6.465%   $164.7652   $164.77   $164.75   $164.80  
  Purchase #4 $217.51   13.322%   $246.4867   $246.49   $246.50   $246.50  
  Purchase #5 $80.31   12.468%   $90.3231   $90.32   $90.30   $90.30  
  Purchase #6 $112.68   11.564%   $125.7103   $125.71   $125.70   $125.70  
  Purchase #7 $245.36   10.707%   $271.6307   $271.63   $271.65   $271.60  
  7 purchase totals = $1,144.95       $1,259.5166   $1,259.52   $1,259.50   $1,259.50