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 $23.75   9.763%   $26.0687   $26.07   $26.05   $26.10  
  Purchase #2 $210.89   12.165%   $236.5448   $236.54   $236.55   $236.50  
  Purchase #3 $62.81   7.681%   $67.6344   $67.63   $67.65   $67.60  
  Purchase #4 $14.93   12.617%   $16.8137   $16.81   $16.80   $16.80  
  Purchase #5 $179.91   13.325%   $203.883   $203.88   $203.90   $203.90  
  Purchase #6 $116.79   10.695%   $129.2807   $129.28   $129.30   $129.30  
  Purchase #7 $68.79   9.514%   $75.3347   $75.33   $75.35   $75.30  
  7 purchase totals = $677.87       $755.5600   $755.54   $755.60   $755.50