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 $58.53   4.139%   $60.9526   $60.95   $60.95   $61.00  
  Purchase #2 $249.38   4.763%   $261.258   $261.26   $261.25   $261.30  
  Purchase #3 $166.34   4.185%   $173.3013   $173.30   $173.30   $173.30  
  Purchase #4 $35.30   5.864%   $37.37   $37.37   $37.35   $37.40  
  Purchase #5 $85.32   12.600%   $96.0703   $96.07   $96.05   $96.10  
  Purchase #6 $115.48   13.398%   $130.952   $130.95   $130.95   $131.00  
  Purchase #7 $55.52   13.228%   $62.8642   $62.86   $62.85   $62.90  
  7 purchase totals = $765.87       $822.7684   $822.76   $822.70   $823.00