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 $112.85   4.821%   $118.2905   $118.29   $118.30   $118.30  
  Purchase #2 $50.76   5.701%   $53.6538   $53.65   $53.65   $53.70  
  Purchase #3 $108.92   12.163%   $122.1679   $122.17   $122.15   $122.20  
  Purchase #4 $41.43   7.723%   $44.6296   $44.63   $44.65   $44.60  
  Purchase #5 $237.78   13.620%   $270.1656   $270.17   $270.15   $270.20  
  Purchase #6 $229.89   10.105%   $253.1204   $253.12   $253.10   $253.10  
  Purchase #7 $192.66   3.235%   $198.8926   $198.89   $198.90   $198.90  
  7 purchase totals = $974.29       $1,060.9204   $1,060.92   $1,060.90   $1,061.00