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 $156.38   12.687%   $176.2199   $176.22   $176.20   $176.20  
  Purchase #2 $163.34   11.757%   $182.5439   $182.54   $182.55   $182.50  
  Purchase #3 $192.36   5.276%   $202.5089   $202.51   $202.50   $202.50  
  Purchase #4 $244.61   12.554%   $275.3183   $275.32   $275.30   $275.30  
  Purchase #5 $87.38   5.736%   $92.3921   $92.39   $92.40   $92.40  
  Purchase #6 $77.61   10.230%   $85.5495   $85.55   $85.55   $85.50  
  Purchase #7 $233.35   6.176%   $247.7617   $247.76   $247.75   $247.80  
  7 purchase totals = $1,155.03       $1,262.2943   $1,262.29   $1,262.25   $1,262.20