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 $168.65   10.499%   $186.3566   $186.36   $186.35   $186.40  
  Purchase #2 $161.98   7.671%   $174.4055   $174.41   $174.40   $174.40  
  Purchase #3 $50.86   9.375%   $55.6281   $55.63   $55.65   $55.60  
  Purchase #4 $101.69   13.565%   $115.4842   $115.48   $115.50   $115.50  
  Purchase #5 $142.75   6.104%   $151.4635   $151.46   $151.45   $151.50  
  Purchase #6 $233.65   3.147%   $241.003   $241.00   $241.00   $241.00  
  Purchase #7 $17.59   12.161%   $19.7291   $19.73   $19.75   $19.70  
  7 purchase totals = $877.17       $944.0700   $944.07   $944.10   $944.10