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 $212.49   11.762%   $237.4831   $237.48   $237.50   $237.50  
  Purchase #2 $54.54   8.810%   $59.345   $59.35   $59.35   $59.30  
  Purchase #3 $44.70   9.243%   $48.8316   $48.83   $48.85   $48.80  
  Purchase #4 $115.75   8.204%   $125.2461   $125.25   $125.25   $125.20  
  Purchase #5 $244.64   4.116%   $254.7094   $254.71   $254.70   $254.70  
  Purchase #6 $27.89   9.754%   $30.6104   $30.61   $30.60   $30.60  
  Purchase #7 $83.97   11.310%   $93.467   $93.47   $93.45   $93.50  
  7 purchase totals = $783.98       $849.6926   $849.70   $849.70   $849.60