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 $226.87   8.761%   $246.7461   $246.75   $246.75   $246.70  
  Purchase #2 $10.70   10.413%   $11.8142   $11.81   $11.80   $11.80  
  Purchase #3 $135.40   6.307%   $143.9397   $143.94   $143.95   $143.90  
  Purchase #4 $90.63   7.556%   $97.478   $97.48   $97.50   $97.50  
  Purchase #5 $214.97   12.861%   $242.6173   $242.62   $242.60   $242.60  
  Purchase #6 $133.27   7.520%   $143.2919   $143.29   $143.30   $143.30  
  Purchase #7 $144.95   12.787%   $163.4848   $163.48   $163.50   $163.50  
  7 purchase totals = $956.79       $1,049.3720   $1,049.37   $1,049.40   $1,049.30