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 $116.25   6.632%   $123.9597   $123.96   $123.95   $124.00  
  Purchase #2 $174.41   3.124%   $179.8586   $179.86   $179.85   $179.90  
  Purchase #3 $68.34   10.782%   $75.7084   $75.71   $75.70   $75.70  
  Purchase #4 $95.59   4.727%   $100.1085   $100.11   $100.10   $100.10  
  Purchase #5 $119.95   7.691%   $129.1754   $129.18   $129.20   $129.20  
  Purchase #6 $109.87   3.610%   $113.8363   $113.84   $113.85   $113.80  
  Purchase #7 $239.60   11.227%   $266.4999   $266.50   $266.50   $266.50  
  7 purchase totals = $924.01       $989.1468   $989.16   $989.15   $989.20