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	$237.53	8.243%	$257.1096	$257.11	$257.10	$257.10
Purchase #2	$229.50	13.718%	$260.9828	$260.98	$261.00	$261.00
Purchase #3	$116.51	9.198%	$127.2266	$127.23	$127.25	$127.20
Purchase #4	$220.91	11.240%	$245.7403	$245.74	$245.75	$245.70
Purchase #5	$153.42	7.300%	$164.6197	$164.62	$164.60	$164.60
Purchase #6	$250.25	3.803%	$259.767	$259.77	$259.75	$259.80
Purchase #7	$16.71	10.243%	$18.4216	$18.42	$18.40	$18.40
7 purchase totals =	$1,224.83		$1,333.8676	$1,333.87	$1,333.85	$1,333.80