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	$127.38	12.859%	$143.7598	$143.76	$143.75	$143.80
Purchase #2	$177.97	12.543%	$200.2928	$200.29	$200.30	$200.30
Purchase #3	$168.38	11.258%	$187.3362	$187.34	$187.35	$187.30
Purchase #4	$192.87	10.682%	$213.4724	$213.47	$213.45	$213.50
Purchase #5	$82.92	12.573%	$93.3455	$93.35	$93.35	$93.30
Purchase #6	$59.64	12.127%	$66.8725	$66.87	$66.85	$66.90
Purchase #7	$242.34	3.510%	$250.8461	$250.85	$250.85	$250.80
7 purchase totals =	$1,051.50		$1,155.9253	$1,155.93	$1,155.90	$1,155.90