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 $62.87   10.550%   $69.5028   $69.50   $69.50   $69.50  
  Purchase #2 $152.50   6.809%   $162.8837   $162.88   $162.90   $162.90  
  Purchase #3 $67.92   12.294%   $76.2701   $76.27   $76.25   $76.30  
  Purchase #4 $73.35   7.333%   $78.7288   $78.73   $78.75   $78.70  
  Purchase #5 $228.26   7.297%   $244.9161   $244.92   $244.90   $244.90  
  Purchase #6 $169.40   9.291%   $185.139   $185.14   $185.15   $185.10  
  Purchase #7 $24.28   5.162%   $25.5333   $25.53   $25.55   $25.50  
  7 purchase totals = $778.58       $842.9738   $842.97   $843.00   $842.90