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 $227.74   8.325%   $246.6994   $246.70   $246.70   $246.70  
  Purchase #2 $116.73   5.285%   $122.8992   $122.90   $122.90   $122.90  
  Purchase #3 $140.75   6.348%   $149.6848   $149.68   $149.70   $149.70  
  Purchase #4 $132.53   6.770%   $141.5023   $141.50   $141.50   $141.50  
  Purchase #5 $197.81   3.185%   $204.1102   $204.11   $204.10   $204.10  
  Purchase #6 $231.99   4.633%   $242.7381   $242.74   $242.75   $242.70  
  Purchase #7 $133.43   9.857%   $146.5822   $146.58   $146.60   $146.60  
  7 purchase totals = $1,180.98       $1,254.2162   $1,254.21   $1,254.25   $1,254.20