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 $174.27   11.628%   $194.5341   $194.53   $194.55   $194.50  
  Purchase #2 $28.62   3.663%   $29.6684   $29.67   $29.65   $29.70  
  Purchase #3 $57.95   12.536%   $65.2146   $65.21   $65.20   $65.20  
  Purchase #4 $184.99   5.552%   $195.2606   $195.26   $195.25   $195.30  
  Purchase #5 $35.82   6.821%   $38.2633   $38.26   $38.25   $38.30  
  Purchase #6 $80.59   12.622%   $90.7621   $90.76   $90.75   $90.80  
  Purchase #7 $192.81   6.826%   $205.9712   $205.97   $205.95   $206.00  
  7 purchase totals = $755.05       $819.6743   $819.66   $819.60   $819.80