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	$170.82	4.251%	$178.0816	$178.08	$178.10	$178.10
Purchase #2	$205.46	8.768%	$223.4747	$223.47	$223.45	$223.50
Purchase #3	$242.66	3.235%	$250.5101	$250.51	$250.50	$250.50
Purchase #4	$245.71	13.677%	$279.3158	$279.32	$279.30	$279.30
Purchase #5	$154.33	5.308%	$162.5218	$162.52	$162.50	$162.50
Purchase #6	$229.79	5.685%	$242.8536	$242.85	$242.85	$242.90
Purchase #7	$146.95	11.830%	$164.3342	$164.33	$164.35	$164.30
7 purchase totals =	$1,395.72		$1,501.0918	$1,501.08	$1,501.05	$1,501.10