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 $197.77   4.186%   $206.0487   $206.05   $206.05   $206.00  
  Purchase #2 $157.35   13.726%   $178.9479   $178.95   $178.95   $178.90  
  Purchase #3 $215.47   11.373%   $239.9754   $239.98   $240.00   $240.00  
  Purchase #4 $241.73   11.362%   $269.1954   $269.20   $269.20   $269.20  
  Purchase #5 $124.76   4.181%   $129.9762   $129.98   $130.00   $130.00  
  Purchase #6 $178.85   3.145%   $184.4748   $184.47   $184.45   $184.50  
  Purchase #7 $113.50   3.318%   $117.2659   $117.27   $117.25   $117.30  
  7 purchase totals = $1,229.43       $1,325.8843   $1,325.90   $1,325.90   $1,325.90