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 $36.97   3.549%   $38.2821   $38.28   $38.30   $38.30  
  Purchase #2 $113.38   3.430%   $117.2689   $117.27   $117.25   $117.30  
  Purchase #3 $185.95   10.794%   $206.0214   $206.02   $206.00   $206.00  
  Purchase #4 $68.69   11.766%   $76.7721   $76.77   $76.75   $76.80  
  Purchase #5 $235.53   13.103%   $266.3915   $266.39   $266.40   $266.40  
  Purchase #6 $234.50   3.190%   $241.9806   $241.98   $242.00   $242.00  
  Purchase #7 $112.94   3.259%   $116.6207   $116.62   $116.60   $116.60  
  7 purchase totals = $987.96       $1,063.3373   $1,063.33   $1,063.30   $1,063.40