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 $190.39   3.833%   $197.6876   $197.69   $197.70   $197.70  
  Purchase #2 $248.80   5.284%   $261.9466   $261.95   $261.95   $261.90  
  Purchase #3 $14.33   10.763%   $15.8723   $15.87   $15.85   $15.90  
  Purchase #4 $146.37   6.380%   $155.7084   $155.71   $155.70   $155.70  
  Purchase #5 $116.98   4.411%   $122.14   $122.14   $122.15   $122.10  
  Purchase #6 $118.64   11.470%   $132.248   $132.25   $132.25   $132.20  
  Purchase #7 $105.60   9.419%   $115.5465   $115.55   $115.55   $115.50  
  7 purchase totals = $941.11       $1,001.1494   $1,001.16   $1,001.15   $1,001.00