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 $176.68   10.536%   $195.295   $195.30   $195.30   $195.30  
  Purchase #2 $23.69   13.189%   $26.8145   $26.81   $26.80   $26.80  
  Purchase #3 $236.88   6.228%   $251.6329   $251.63   $251.65   $251.60  
  Purchase #4 $235.45   7.672%   $253.5137   $253.51   $253.50   $253.50  
  Purchase #5 $208.34   13.231%   $235.9055   $235.91   $235.90   $235.90  
  Purchase #6 $63.47   10.481%   $70.1223   $70.12   $70.10   $70.10  
  Purchase #7 $209.27   7.670%   $225.321   $225.32   $225.30   $225.30  
  7 purchase totals = $1,153.78       $1,258.6049   $1,258.60   $1,258.55   $1,258.50