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 $44.88   4.287%   $46.804   $46.80   $46.80   $46.80  
  Purchase #2 $14.31   10.710%   $15.8426   $15.84   $15.85   $15.80  
  Purchase #3 $113.51   5.435%   $119.6793   $119.68   $119.70   $119.70  
  Purchase #4 $178.63   6.165%   $189.6425   $189.64   $189.65   $189.60  
  Purchase #5 $128.33   11.807%   $143.4819   $143.48   $143.50   $143.50  
  Purchase #6 $123.97   6.439%   $131.9524   $131.95   $131.95   $132.00  
  Purchase #7 $247.62   5.490%   $261.2143   $261.21   $261.20   $261.20  
  7 purchase totals = $851.25       $908.6170   $908.60   $908.65   $908.60