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 $90.82   12.492%   $102.1652   $102.17   $102.15   $102.20  
  Purchase #2 $78.54   10.318%   $86.6438   $86.64   $86.65   $86.60  
  Purchase #3 $58.84   6.788%   $62.8341   $62.83   $62.85   $62.80  
  Purchase #4 $14.75   6.498%   $15.7085   $15.71   $15.70   $15.70  
  Purchase #5 $85.51   6.444%   $91.0203   $91.02   $91.00   $91.00  
  Purchase #6 $195.98   3.873%   $203.5703   $203.57   $203.55   $203.60  
  Purchase #7 $236.27   10.495%   $261.0665   $261.07   $261.05   $261.10  
  7 purchase totals = $760.71       $823.0087   $823.01   $822.95   $823.00