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 $49.41   10.271%   $54.4849   $54.48   $54.50   $54.50  
  Purchase #2 $123.66   4.824%   $129.6254   $129.63   $129.65   $129.60  
  Purchase #3 $15.64   13.399%   $17.7356   $17.74   $17.75   $17.70  
  Purchase #4 $41.52   13.603%   $47.168   $47.17   $47.15   $47.20  
  Purchase #5 $217.39   10.225%   $239.6181   $239.62   $239.60   $239.60  
  Purchase #6 $67.78   9.587%   $74.2781   $74.28   $74.30   $74.30  
  Purchase #7 $55.75   6.747%   $59.5115   $59.51   $59.50   $59.50  
  7 purchase totals = $571.15       $622.4216   $622.43   $622.45   $622.40