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 $240.45   6.702%   $256.565   $256.57   $256.55   $256.60  
  Purchase #2 $127.39   4.703%   $133.3812   $133.38   $133.40   $133.40  
  Purchase #3 $48.46   8.561%   $52.6087   $52.61   $52.60   $52.60  
  Purchase #4 $10.95   4.845%   $11.4805   $11.48   $11.50   $11.50  
  Purchase #5 $177.84   9.617%   $194.9429   $194.94   $194.95   $194.90  
  Purchase #6 $184.60   9.779%   $202.652   $202.65   $202.65   $202.70  
  Purchase #7 $96.83   11.163%   $107.6391   $107.64   $107.65   $107.60  
  7 purchase totals = $886.52       $959.2694   $959.27   $959.30   $959.30