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 $212.86   12.865%   $240.2444   $240.24   $240.25   $240.20  
  Purchase #2 $235.43   13.345%   $266.8481   $266.85   $266.85   $266.80  
  Purchase #3 $206.38   5.674%   $218.09   $218.09   $218.10   $218.10  
  Purchase #4 $244.86   3.671%   $253.8488   $253.85   $253.85   $253.80  
  Purchase #5 $116.75   11.857%   $130.593   $130.59   $130.60   $130.60  
  Purchase #6 $136.69   12.216%   $153.3881   $153.39   $153.40   $153.40  
  Purchase #7 $222.96   12.406%   $250.6204   $250.62   $250.60   $250.60  
  7 purchase totals = $1,375.93       $1,513.6328   $1,513.63   $1,513.65   $1,513.50