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 $227.86   9.559%   $249.6411   $249.64   $249.65   $249.60  
  Purchase #2 $14.35   13.608%   $16.3027   $16.30   $16.30   $16.30  
  Purchase #3 $96.83   5.612%   $102.2641   $102.26   $102.25   $102.30  
  Purchase #4 $42.64   9.325%   $46.6162   $46.62   $46.60   $46.60  
  Purchase #5 $198.98   4.717%   $208.3659   $208.37   $208.35   $208.40  
  Purchase #6 $166.90   6.278%   $177.378   $177.38   $177.40   $177.40  
  Purchase #7 $154.40   4.257%   $160.9728   $160.97   $160.95   $161.00  
  7 purchase totals = $901.96       $961.5408   $961.54   $961.50   $961.60