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 $232.96   10.148%   $256.6008   $256.60   $256.60   $256.60  
  Purchase #2 $45.47   8.796%   $49.4695   $49.47   $49.45   $49.50  
  Purchase #3 $111.83   11.166%   $124.3169   $124.32   $124.30   $124.30  
  Purchase #4 $208.94   10.472%   $230.8202   $230.82   $230.80   $230.80  
  Purchase #5 $187.63   11.638%   $209.4664   $209.47   $209.45   $209.50  
  Purchase #6 $33.66   9.737%   $36.9375   $36.94   $36.95   $36.90  
  Purchase #7 $8.73   11.165%   $9.7047   $9.70   $9.70   $9.70  
  7 purchase totals = $829.22       $917.3160   $917.32   $917.25   $917.30