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 $239.43   6.513%   $255.0241   $255.02   $255.00   $255.00  
  Purchase #2 $55.55   10.263%   $61.2511   $61.25   $61.25   $61.30  
  Purchase #3 $215.60   12.565%   $242.6901   $242.69   $242.70   $242.70  
  Purchase #4 $245.68   12.378%   $276.0903   $276.09   $276.10   $276.10  
  Purchase #5 $136.60   11.423%   $152.2038   $152.20   $152.20   $152.20  
  Purchase #6 $92.38   13.469%   $104.8227   $104.82   $104.80   $104.80  
  Purchase #7 $85.74   8.738%   $93.232   $93.23   $93.25   $93.20  
  7 purchase totals = $1,070.98       $1,185.3141   $1,185.30   $1,185.30   $1,185.30