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 $226.46   4.792%   $237.312   $237.31   $237.30   $237.30  
  Purchase #2 $58.55   8.143%   $63.3177   $63.32   $63.30   $63.30  
  Purchase #3 $51.81   8.259%   $56.089   $56.09   $56.10   $56.10  
  Purchase #4 $237.99   7.411%   $255.6274   $255.63   $255.65   $255.60  
  Purchase #5 $200.46   13.259%   $227.039   $227.04   $227.05   $227.00  
  Purchase #6 $73.93   3.837%   $76.7667   $76.77   $76.75   $76.80  
  Purchase #7 $95.34   9.200%   $104.1113   $104.11   $104.10   $104.10  
  7 purchase totals = $944.54       $1,020.2631   $1,020.27   $1,020.25   $1,020.20