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 $216.89   11.789%   $242.4592   $242.46   $242.45   $242.50  
  Purchase #2 $129.98   13.597%   $147.6534   $147.65   $147.65   $147.70  
  Purchase #3 $22.61   12.175%   $25.3628   $25.36   $25.35   $25.40  
  Purchase #4 $220.71   3.781%   $229.055   $229.06   $229.05   $229.10  
  Purchase #5 $184.69   3.281%   $190.7497   $190.75   $190.75   $190.70  
  Purchase #6 $190.63   10.390%   $210.4365   $210.44   $210.45   $210.40  
  Purchase #7 $214.63   4.662%   $224.6361   $224.64   $224.65   $224.60  
  7 purchase totals = $1,180.14       $1,270.3527   $1,270.36   $1,270.35   $1,270.40