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 $234.95   4.581%   $245.7131   $245.71   $245.70   $245.70  
  Purchase #2 $184.42   11.269%   $205.2023   $205.20   $205.20   $205.20  
  Purchase #3 $232.71   12.290%   $261.3101   $261.31   $261.30   $261.30  
  Purchase #4 $113.51   10.380%   $125.2923   $125.29   $125.30   $125.30  
  Purchase #5 $184.32   4.501%   $192.6162   $192.62   $192.60   $192.60  
  Purchase #6 $187.63   9.253%   $204.9914   $204.99   $205.00   $205.00  
  Purchase #7 $62.79   5.421%   $66.1938   $66.19   $66.20   $66.20  
  7 purchase totals = $1,200.33       $1,301.3192   $1,301.31   $1,301.30   $1,301.30