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 $161.68   12.727%   $182.257   $182.26   $182.25   $182.30  
  Purchase #2 $50.33   8.263%   $54.4888   $54.49   $54.50   $54.50  
  Purchase #3 $81.95   12.105%   $91.87   $91.87   $91.85   $91.90  
  Purchase #4 $217.38   11.604%   $242.6048   $242.60   $242.60   $242.60  
  Purchase #5 $245.30   13.173%   $277.6134   $277.61   $277.60   $277.60  
  Purchase #6 $209.61   4.328%   $218.6819   $218.68   $218.70   $218.70  
  Purchase #7 $162.84   12.626%   $183.4002   $183.40   $183.40   $183.40  
  7 purchase totals = $1,129.09       $1,250.9161   $1,250.91   $1,250.90   $1,251.00