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 $186.63   6.426%   $198.6228   $198.62   $198.60   $198.60  
  Purchase #2 $60.96   5.508%   $64.3177   $64.32   $64.30   $64.30  
  Purchase #3 $95.65   11.614%   $106.7588   $106.76   $106.75   $106.80  
  Purchase #4 $199.85   3.113%   $206.0713   $206.07   $206.05   $206.10  
  Purchase #5 $89.73   8.105%   $97.0026   $97.00   $97.00   $97.00  
  Purchase #6 $214.73   6.594%   $228.8893   $228.89   $228.90   $228.90  
  Purchase #7 $140.49   13.264%   $159.1246   $159.12   $159.10   $159.10  
  7 purchase totals = $988.04       $1,060.7871   $1,060.78   $1,060.70   $1,060.80