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 $187.83   8.621%   $204.0228   $204.02   $204.00   $204.00  
  Purchase #2 $112.39   11.460%   $125.2699   $125.27   $125.25   $125.30  
  Purchase #3 $59.63   8.639%   $64.7814   $64.78   $64.80   $64.80  
  Purchase #4 $157.76   7.696%   $169.9012   $169.90   $169.90   $169.90  
  Purchase #5 $94.35   4.250%   $98.3599   $98.36   $98.35   $98.40  
  Purchase #6 $80.55   6.597%   $85.8639   $85.86   $85.85   $85.90  
  Purchase #7 $30.41   3.530%   $31.4835   $31.48   $31.50   $31.50  
  7 purchase totals = $722.92       $779.6826   $779.67   $779.65   $779.80