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 $241.82   8.135%   $261.4921   $261.49   $261.50   $261.50  
  Purchase #2 $220.27   4.282%   $229.702   $229.70   $229.70   $229.70  
  Purchase #3 $244.36   12.406%   $274.6753   $274.68   $274.70   $274.70  
  Purchase #4 $169.57   4.144%   $176.597   $176.60   $176.60   $176.60  
  Purchase #5 $227.80   3.138%   $234.9484   $234.95   $234.95   $234.90  
  Purchase #6 $220.98   10.193%   $243.5045   $243.50   $243.50   $243.50  
  Purchase #7 $92.43   8.216%   $100.024   $100.02   $100.00   $100.00  
  7 purchase totals = $1,417.23       $1,520.9433   $1,520.94   $1,520.95   $1,520.90