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	$151.42	3.255%	$156.3487	$156.35	$156.35	$156.30
Purchase #2	$75.66	4.827%	$79.3121	$79.31	$79.30	$79.30
Purchase #3	$80.64	11.543%	$89.9483	$89.95	$89.95	$89.90
Purchase #4	$164.76	8.122%	$178.1418	$178.14	$178.15	$178.10
Purchase #5	$79.27	12.279%	$89.0036	$89.00	$89.00	$89.00
Purchase #6	$124.44	13.733%	$141.5293	$141.53	$141.55	$141.50
Purchase #7	$57.88	3.860%	$60.1142	$60.11	$60.10	$60.10
7 purchase totals =	$734.07		$794.3980	$794.39	$794.40	$794.20