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 $59.67   10.620%   $66.007   $66.01   $66.00   $66.00  
  Purchase #2 $244.98   11.817%   $273.9293   $273.93   $273.95   $273.90  
  Purchase #3 $151.77   9.656%   $166.4249   $166.42   $166.40   $166.40  
  Purchase #4 $195.97   7.289%   $210.2543   $210.25   $210.25   $210.30  
  Purchase #5 $144.45   6.603%   $153.988   $153.99   $154.00   $154.00  
  Purchase #6 $101.62   3.462%   $105.1381   $105.14   $105.15   $105.10  
  Purchase #7 $114.37   13.655%   $129.9872   $129.99   $130.00   $130.00  
  7 purchase totals = $1,012.83       $1,105.7288   $1,105.73   $1,105.75   $1,105.70