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 $248.98   10.798%   $275.8649   $275.86   $275.85   $275.90  
  Purchase #2 $245.93   6.396%   $261.6597   $261.66   $261.65   $261.70  
  Purchase #3 $29.75   9.293%   $32.5147   $32.51   $32.50   $32.50  
  Purchase #4 $117.92   11.489%   $131.4678   $131.47   $131.45   $131.50  
  Purchase #5 $84.28   10.408%   $93.0519   $93.05   $93.05   $93.10  
  Purchase #6 $237.92   5.590%   $251.2197   $251.22   $251.20   $251.20  
  Purchase #7 $220.37   7.307%   $236.4724   $236.47   $236.45   $236.50  
  7 purchase totals = $1,185.15       $1,282.2511   $1,282.24   $1,282.15   $1,282.40