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 $23.49   11.185%   $26.1174   $26.12   $26.10   $26.10  
  Purchase #2 $192.82   9.234%   $210.625   $210.63   $210.65   $210.60  
  Purchase #3 $120.90   10.482%   $133.5727   $133.57   $133.55   $133.60  
  Purchase #4 $63.49   10.571%   $70.2015   $70.20   $70.20   $70.20  
  Purchase #5 $62.32   4.330%   $65.0185   $65.02   $65.00   $65.00  
  Purchase #6 $199.56   12.866%   $225.2354   $225.24   $225.25   $225.20  
  Purchase #7 $229.85   6.164%   $244.018   $244.02   $244.00   $244.00  
  7 purchase totals = $892.43       $974.7885   $974.80   $974.75   $974.70