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 $244.84   11.557%   $273.1362   $273.14   $273.15   $273.10  
  Purchase #2 $208.88   3.340%   $215.8566   $215.86   $215.85   $215.90  
  Purchase #3 $113.38   3.266%   $117.083   $117.08   $117.10   $117.10  
  Purchase #4 $209.49   3.715%   $217.2726   $217.27   $217.25   $217.30  
  Purchase #5 $221.96   12.631%   $249.9958   $250.00   $250.00   $250.00  
  Purchase #6 $151.43   6.399%   $161.12   $161.12   $161.10   $161.10  
  Purchase #7 $173.85   9.488%   $190.3449   $190.34   $190.35   $190.30  
  7 purchase totals = $1,323.83       $1,424.8091   $1,424.81   $1,424.80   $1,424.80