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 $246.71   10.709%   $273.1302   $273.13   $273.15   $273.10  
  Purchase #2 $222.51   6.258%   $236.4347   $236.43   $236.45   $236.40  
  Purchase #3 $149.59   9.790%   $164.2349   $164.23   $164.25   $164.20  
  Purchase #4 $22.99   13.695%   $26.1385   $26.14   $26.15   $26.10  
  Purchase #5 $240.30   4.845%   $251.9425   $251.94   $251.95   $251.90  
  Purchase #6 $235.96   3.439%   $244.0747   $244.07   $244.05   $244.10  
  Purchase #7 $95.75   13.513%   $108.6887   $108.69   $108.70   $108.70  
  7 purchase totals = $1,213.81       $1,304.6442   $1,304.63   $1,304.70   $1,304.50