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 $152.46   6.178%   $161.879   $161.88   $161.90   $161.90  
  Purchase #2 $66.80   3.495%   $69.1347   $69.13   $69.15   $69.10  
  Purchase #3 $164.27   7.389%   $176.4079   $176.41   $176.40   $176.40  
  Purchase #4 $215.63   4.276%   $224.8503   $224.85   $224.85   $224.90  
  Purchase #5 $243.49   9.646%   $266.977   $266.98   $267.00   $267.00  
  Purchase #6 $175.62   3.558%   $181.8686   $181.87   $181.85   $181.90  
  Purchase #7 $146.27   4.434%   $152.7556   $152.76   $152.75   $152.80  
  7 purchase totals = $1,164.54       $1,233.8731   $1,233.88   $1,233.90   $1,234.00