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 $249.97   6.131%   $265.2957   $265.30   $265.30   $265.30  
  Purchase #2 $185.79   12.601%   $209.2014   $209.20   $209.20   $209.20  
  Purchase #3 $112.62   7.642%   $121.2264   $121.23   $121.25   $121.20  
  Purchase #4 $55.73   4.625%   $58.3075   $58.31   $58.30   $58.30  
  Purchase #5 $143.40   7.760%   $154.5278   $154.53   $154.55   $154.50  
  Purchase #6 $32.64   11.374%   $36.3525   $36.35   $36.35   $36.40  
  Purchase #7 $110.61   8.549%   $120.066   $120.07   $120.05   $120.10  
  7 purchase totals = $890.76       $964.9773   $964.99   $965.00   $965.00