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 $162.95   13.862%   $185.5381   $185.54   $185.55   $185.50  
  Purchase #2 $41.92   13.521%   $47.588   $47.59   $47.60   $47.60  
  Purchase #3 $205.94   13.552%   $233.849   $233.85   $233.85   $233.80  
  Purchase #4 $65.63   13.668%   $74.6003   $74.60   $74.60   $74.60  
  Purchase #5 $15.44   9.426%   $16.8954   $16.90   $16.90   $16.90  
  Purchase #6 $187.69   13.597%   $213.2102   $213.21   $213.20   $213.20  
  Purchase #7 $248.62   12.648%   $280.0655   $280.07   $280.05   $280.10  
  7 purchase totals = $928.19       $1,051.7465   $1,051.76   $1,051.75   $1,051.70