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 $47.31   4.496%   $49.4371   $49.44   $49.45   $49.40  
  Purchase #2 $61.59   6.820%   $65.7904   $65.79   $65.80   $65.80  
  Purchase #3 $232.27   5.585%   $245.2423   $245.24   $245.25   $245.20  
  Purchase #4 $157.39   5.271%   $165.686   $165.69   $165.70   $165.70  
  Purchase #5 $54.47   13.378%   $61.757   $61.76   $61.75   $61.80  
  Purchase #6 $248.55   8.197%   $268.9236   $268.92   $268.90   $268.90  
  Purchase #7 $232.44   10.726%   $257.3715   $257.37   $257.35   $257.40  
  7 purchase totals = $1,034.02       $1,114.2079   $1,114.21   $1,114.20   $1,114.20