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 $25.32   4.605%   $26.486   $26.49   $26.50   $26.50  
  Purchase #2 $76.72   6.763%   $81.9086   $81.91   $81.90   $81.90  
  Purchase #3 $184.62   8.783%   $200.8352   $200.84   $200.85   $200.80  
  Purchase #4 $153.88   5.499%   $162.3419   $162.34   $162.35   $162.30  
  Purchase #5 $242.77   6.385%   $258.2709   $258.27   $258.25   $258.30  
  Purchase #6 $241.33   11.709%   $269.5873   $269.59   $269.60   $269.60  
  Purchase #7 $20.97   10.479%   $23.1674   $23.17   $23.15   $23.20  
  7 purchase totals = $945.61       $1,022.5973   $1,022.61   $1,022.60   $1,022.60