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 $63.60   4.294%   $66.331   $66.33   $66.35   $66.30  
  Purchase #2 $197.62   10.162%   $217.7021   $217.70   $217.70   $217.70  
  Purchase #3 $52.44   9.149%   $57.2377   $57.24   $57.25   $57.20  
  Purchase #4 $152.34   10.241%   $167.9411   $167.94   $167.95   $167.90  
  Purchase #5 $114.38   13.215%   $129.4953   $129.50   $129.50   $129.50  
  Purchase #6 $154.46   8.221%   $167.1582   $167.16   $167.15   $167.20  
  Purchase #7 $46.83   5.694%   $49.4965   $49.50   $49.50   $49.50  
  7 purchase totals = $781.67       $855.3619   $855.37   $855.40   $855.30