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 $10.68   6.259%   $11.3485   $11.35   $11.35   $11.30  
  Purchase #2 $74.54   13.167%   $84.3547   $84.35   $84.35   $84.40  
  Purchase #3 $221.95   12.425%   $249.5273   $249.53   $249.55   $249.50  
  Purchase #4 $224.51   11.518%   $250.3691   $250.37   $250.35   $250.40  
  Purchase #5 $5.86   8.123%   $6.336   $6.34   $6.35   $6.30  
  Purchase #6 $217.42   9.336%   $237.7183   $237.72   $237.70   $237.70  
  Purchase #7 $44.83   7.453%   $48.1712   $48.17   $48.15   $48.20  
  7 purchase totals = $799.79       $887.8251   $887.83   $887.80   $887.80