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 $112.67   5.232%   $118.5649   $118.56   $118.55   $118.60  
  Purchase #2 $18.95   6.475%   $20.177   $20.18   $20.20   $20.20  
  Purchase #3 $96.87   11.265%   $107.7824   $107.78   $107.80   $107.80  
  Purchase #4 $207.62   13.358%   $235.3539   $235.35   $235.35   $235.40  
  Purchase #5 $152.63   4.183%   $159.0145   $159.01   $159.00   $159.00  
  Purchase #6 $69.70   8.346%   $75.5172   $75.52   $75.50   $75.50  
  Purchase #7 $236.87   7.379%   $254.3486   $254.35   $254.35   $254.30  
  7 purchase totals = $895.31       $970.7585   $970.75   $970.75   $970.80