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 $246.26   8.211%   $266.4804   $266.48   $266.50   $266.50  
  Purchase #2 $243.64   7.196%   $261.1723   $261.17   $261.15   $261.20  
  Purchase #3 $227.44   6.701%   $242.6808   $242.68   $242.70   $242.70  
  Purchase #4 $217.66   11.841%   $243.4331   $243.43   $243.45   $243.40  
  Purchase #5 $52.74   8.212%   $57.071   $57.07   $57.05   $57.10  
  Purchase #6 $69.84   3.231%   $72.0965   $72.10   $72.10   $72.10  
  Purchase #7 $82.70   10.473%   $91.3612   $91.36   $91.35   $91.40  
  7 purchase totals = $1,140.28       $1,234.2953   $1,234.29   $1,234.30   $1,234.40