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	$89.53	5.346%	$94.3163	$94.32	$94.30	$94.30
Purchase #2	$113.77	12.762%	$128.2893	$128.29	$128.30	$128.30
Purchase #3	$166.87	3.350%	$172.4601	$172.46	$172.45	$172.50
Purchase #4	$58.88	10.793%	$65.2349	$65.23	$65.25	$65.20
Purchase #5	$46.71	7.403%	$50.1679	$50.17	$50.15	$50.20
Purchase #6	$14.76	4.632%	$15.4437	$15.44	$15.45	$15.40
Purchase #7	$221.51	9.396%	$242.3231	$242.32	$242.30	$242.30
7 purchase totals =	$712.03		$768.2353	$768.23	$768.20	$768.20