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 $87.69   12.307%   $98.482   $98.48   $98.50   $98.50  
  Purchase #2 $32.26   4.351%   $33.6636   $33.66   $33.65   $33.70  
  Purchase #3 $140.90   11.233%   $156.7273   $156.73   $156.75   $156.70  
  Purchase #4 $175.85   12.511%   $197.8506   $197.85   $197.85   $197.90  
  Purchase #5 $249.45   5.774%   $263.8532   $263.85   $263.85   $263.90  
  Purchase #6 $185.95   12.175%   $208.5894   $208.59   $208.60   $208.60  
  Purchase #7 $111.87   9.475%   $122.4697   $122.47   $122.45   $122.50  
  7 purchase totals = $983.97       $1,081.6358   $1,081.63   $1,081.65   $1,081.80