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 $44.83   6.472%   $47.7314   $47.73   $47.75   $47.70  
  Purchase #2 $124.93   11.558%   $139.3694   $139.37   $139.35   $139.40  
  Purchase #3 $60.57   12.662%   $68.2394   $68.24   $68.25   $68.20  
  Purchase #4 $75.93   9.693%   $83.2899   $83.29   $83.30   $83.30  
  Purchase #5 $41.68   12.259%   $46.7896   $46.79   $46.80   $46.80  
  Purchase #6 $172.84   7.344%   $185.5334   $185.53   $185.55   $185.50  
  Purchase #7 $176.46   10.400%   $194.8118   $194.81   $194.80   $194.80  
  7 purchase totals = $697.24       $765.7649   $765.76   $765.80   $765.70