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 $110.67   13.676%   $125.8052   $125.81   $125.80   $125.80  
  Purchase #2 $231.41   12.729%   $260.8662   $260.87   $260.85   $260.90  
  Purchase #3 $80.46   5.131%   $84.5884   $84.59   $84.60   $84.60  
  Purchase #4 $35.47   3.796%   $36.8164   $36.82   $36.80   $36.80  
  Purchase #5 $212.26   8.237%   $229.7439   $229.74   $229.75   $229.70  
  Purchase #6 $64.88   10.200%   $71.4978   $71.50   $71.50   $71.50  
  Purchase #7 $114.30   3.832%   $118.68   $118.68   $118.70   $118.70  
  7 purchase totals = $849.45       $927.9979   $928.01   $928.00   $928.00