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 $80.25   4.491%   $83.854   $83.85   $83.85   $83.90  
  Purchase #2 $183.95   6.391%   $195.7062   $195.71   $195.70   $195.70  
  Purchase #3 $114.45   4.492%   $119.5911   $119.59   $119.60   $119.60  
  Purchase #4 $80.92   8.292%   $87.6299   $87.63   $87.65   $87.60  
  Purchase #5 $177.27   9.560%   $194.217   $194.22   $194.20   $194.20  
  Purchase #6 $152.50   6.490%   $162.3973   $162.40   $162.40   $162.40  
  Purchase #7 $237.45   11.127%   $263.8711   $263.87   $263.85   $263.90  
  7 purchase totals = $1,026.79       $1,107.2666   $1,107.27   $1,107.25   $1,107.30