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 $209.53   8.777%   $227.9204   $227.92   $227.90   $227.90  
  Purchase #2 $237.92   10.735%   $263.4607   $263.46   $263.45   $263.50  
  Purchase #3 $6.32   12.689%   $7.1219   $7.12   $7.10   $7.10  
  Purchase #4 $191.75   13.338%   $217.3256   $217.33   $217.35   $217.30  
  Purchase #5 $223.63   5.821%   $236.6475   $236.65   $236.65   $236.60  
  Purchase #6 $76.27   13.565%   $86.616   $86.62   $86.60   $86.60  
  Purchase #7 $176.46   3.459%   $182.5638   $182.56   $182.55   $182.60  
  7 purchase totals = $1,121.88       $1,221.6559   $1,221.66   $1,221.60   $1,221.60