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 $53.49   11.702%   $59.7494   $59.75   $59.75   $59.70  
  Purchase #2 $131.73   12.496%   $148.191   $148.19   $148.20   $148.20  
  Purchase #3 $27.44   5.856%   $29.0469   $29.05   $29.05   $29.00  
  Purchase #4 $100.75   13.791%   $114.6444   $114.64   $114.65   $114.60  
  Purchase #5 $169.86   6.191%   $180.376   $180.38   $180.40   $180.40  
  Purchase #6 $61.45   8.581%   $66.723   $66.72   $66.70   $66.70  
  Purchase #7 $191.69   6.794%   $204.7134   $204.71   $204.70   $204.70  
  7 purchase totals = $736.41       $803.4441   $803.44   $803.45   $803.30