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 $54.68   9.181%   $59.7002   $59.70   $59.70   $59.70  
  Purchase #2 $162.49   8.851%   $176.872   $176.87   $176.85   $176.90  
  Purchase #3 $40.99   6.114%   $43.4961   $43.50   $43.50   $43.50  
  Purchase #4 $38.66   4.448%   $40.3796   $40.38   $40.40   $40.40  
  Purchase #5 $101.98   4.592%   $106.6629   $106.66   $106.65   $106.70  
  Purchase #6 $147.63   11.560%   $164.696   $164.70   $164.70   $164.70  
  Purchase #7 $177.85   5.199%   $187.0964   $187.10   $187.10   $187.10  
  7 purchase totals = $724.28       $778.9032   $778.91   $778.90   $779.00