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 $14.86   3.842%   $15.4309   $15.43   $15.45   $15.40  
  Purchase #2 $198.97   9.535%   $217.9418   $217.94   $217.95   $217.90  
  Purchase #3 $208.41   5.844%   $220.5895   $220.59   $220.60   $220.60  
  Purchase #4 $195.86   13.721%   $222.734   $222.73   $222.75   $222.70  
  Purchase #5 $72.27   4.230%   $75.327   $75.33   $75.35   $75.30  
  Purchase #6 $203.54   11.611%   $227.173   $227.17   $227.15   $227.20  
  Purchase #7 $211.63   8.309%   $229.2143   $229.21   $229.20   $229.20  
  7 purchase totals = $1,105.54       $1,208.4105   $1,208.40   $1,208.45   $1,208.30