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 $48.46   12.287%   $54.4143   $54.41   $54.40   $54.40  
  Purchase #2 $63.38   5.757%   $67.0288   $67.03   $67.05   $67.00  
  Purchase #3 $100.44   10.382%   $110.8677   $110.87   $110.85   $110.90  
  Purchase #4 $32.44   5.685%   $34.2842   $34.28   $34.30   $34.30  
  Purchase #5 $95.50   9.134%   $104.223   $104.22   $104.20   $104.20  
  Purchase #6 $199.85   8.636%   $217.109   $217.11   $217.10   $217.10  
  Purchase #7 $202.48   11.258%   $225.2752   $225.28   $225.30   $225.30  
  7 purchase totals = $742.55       $813.2022   $813.20   $813.20   $813.20