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 $69.65   9.843%   $76.5056   $76.51   $76.50   $76.50  
  Purchase #2 $115.82   6.151%   $122.9441   $122.94   $122.95   $122.90  
  Purchase #3 $43.76   5.607%   $46.2136   $46.21   $46.20   $46.20  
  Purchase #4 $129.66   13.274%   $146.8711   $146.87   $146.85   $146.90  
  Purchase #5 $146.59   8.823%   $159.5236   $159.52   $159.50   $159.50  
  Purchase #6 $226.75   6.243%   $240.906   $240.91   $240.90   $240.90  
  Purchase #7 $114.52   11.351%   $127.5192   $127.52   $127.50   $127.50  
  7 purchase totals = $846.75       $920.4832   $920.48   $920.40   $920.40