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 $208.92   8.218%   $226.089   $226.09   $226.10   $226.10  
  Purchase #2 $26.63   12.372%   $29.9247   $29.92   $29.90   $29.90  
  Purchase #3 $23.94   6.819%   $25.5725   $25.57   $25.55   $25.60  
  Purchase #4 $217.67   3.798%   $225.9371   $225.94   $225.95   $225.90  
  Purchase #5 $115.93   13.488%   $131.5666   $131.57   $131.55   $131.60  
  Purchase #6 $124.27   7.550%   $133.6524   $133.65   $133.65   $133.70  
  Purchase #7 $189.25   5.761%   $200.1527   $200.15   $200.15   $200.20  
  7 purchase totals = $906.61       $972.8950   $972.89   $972.85   $973.00