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 $236.27   6.801%   $252.3387   $252.34   $252.35   $252.30  
  Purchase #2 $59.44   10.650%   $65.7704   $65.77   $65.75   $65.80  
  Purchase #3 $61.83   10.468%   $68.3024   $68.30   $68.30   $68.30  
  Purchase #4 $182.40   8.211%   $197.3769   $197.38   $197.40   $197.40  
  Purchase #5 $233.37   5.399%   $245.9696   $245.97   $245.95   $246.00  
  Purchase #6 $138.93   11.843%   $155.3835   $155.38   $155.40   $155.40  
  Purchase #7 $44.64   11.183%   $49.6321   $49.63   $49.65   $49.60  
  7 purchase totals = $956.88       $1,034.7736   $1,034.77   $1,034.80   $1,034.80