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 $106.46   11.774%   $118.9946   $118.99   $119.00   $119.00  
  Purchase #2 $151.85   8.808%   $165.2249   $165.22   $165.20   $165.20  
  Purchase #3 $227.39   3.570%   $235.5078   $235.51   $235.50   $235.50  
  Purchase #4 $234.54   13.548%   $266.3155   $266.32   $266.30   $266.30  
  Purchase #5 $249.95   7.872%   $269.6261   $269.63   $269.65   $269.60  
  Purchase #6 $196.98   10.356%   $217.3792   $217.38   $217.40   $217.40  
  Purchase #7 $89.46   4.492%   $93.4785   $93.48   $93.50   $93.50  
  7 purchase totals = $1,256.63       $1,366.5266   $1,366.53   $1,366.55   $1,366.50