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 $244.75   12.204%   $274.6193   $274.62   $274.60   $274.60  
  Purchase #2 $68.66   7.613%   $73.8871   $73.89   $73.90   $73.90  
  Purchase #3 $223.63   12.289%   $251.1119   $251.11   $251.10   $251.10  
  Purchase #4 $206.55   10.306%   $227.837   $227.84   $227.85   $227.80  
  Purchase #5 $113.48   12.182%   $127.3041   $127.30   $127.30   $127.30  
  Purchase #6 $86.45   10.339%   $95.3881   $95.39   $95.40   $95.40  
  Purchase #7 $168.43   5.131%   $177.0721   $177.07   $177.05   $177.10  
  7 purchase totals = $1,111.95       $1,227.2196   $1,227.22   $1,227.20   $1,227.20