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 $84.26   11.424%   $93.8859   $93.89   $93.90   $93.90  
  Purchase #2 $233.59   9.868%   $256.6407   $256.64   $256.65   $256.60  
  Purchase #3 $55.61   3.549%   $57.5836   $57.58   $57.60   $57.60  
  Purchase #4 $49.42   7.380%   $53.0672   $53.07   $53.05   $53.10  
  Purchase #5 $53.28   4.233%   $55.5353   $55.54   $55.55   $55.50  
  Purchase #6 $76.99   8.682%   $83.6743   $83.67   $83.65   $83.70  
  Purchase #7 $197.38   4.300%   $205.8673   $205.87   $205.85   $205.90  
  7 purchase totals = $750.53       $806.2543   $806.26   $806.25   $806.30