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 $95.54   12.263%   $107.2561   $107.26   $107.25   $107.30  
  Purchase #2 $119.96   10.299%   $132.3147   $132.31   $132.30   $132.30  
  Purchase #3 $224.26   5.498%   $236.5898   $236.59   $236.60   $236.60  
  Purchase #4 $92.76   8.165%   $100.3339   $100.33   $100.35   $100.30  
  Purchase #5 $24.38   10.497%   $26.9392   $26.94   $26.95   $26.90  
  Purchase #6 $92.29   6.319%   $98.1218   $98.12   $98.10   $98.10  
  Purchase #7 $184.51   6.143%   $195.8444   $195.84   $195.85   $195.80  
  7 purchase totals = $833.70       $897.3999   $897.39   $897.40   $897.30