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 $86.39   8.454%   $93.6934   $93.69   $93.70   $93.70  
  Purchase #2 $198.99   3.781%   $206.5138   $206.51   $206.50   $206.50  
  Purchase #3 $97.44   4.382%   $101.7098   $101.71   $101.70   $101.70  
  Purchase #4 $247.75   7.660%   $266.7277   $266.73   $266.75   $266.70  
  Purchase #5 $222.33   6.529%   $236.8459   $236.85   $236.85   $236.80  
  Purchase #6 $189.62   4.111%   $197.4153   $197.42   $197.40   $197.40  
  Purchase #7 $111.44   10.686%   $123.3485   $123.35   $123.35   $123.30  
  7 purchase totals = $1,153.96       $1,226.2544   $1,226.26   $1,226.25   $1,226.10