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	$29.28	13.200%	$33.145	$33.15	$33.15	$33.10
Purchase #2	$65.90	4.792%	$69.0579	$69.06	$69.05	$69.10
Purchase #3	$122.31	4.707%	$128.0671	$128.07	$128.05	$128.10
Purchase #4	$113.72	6.175%	$120.7422	$120.74	$120.75	$120.70
Purchase #5	$154.94	12.112%	$173.7063	$173.71	$173.70	$173.70
Purchase #6	$117.27	8.580%	$127.3318	$127.33	$127.35	$127.30
Purchase #7	$18.45	13.333%	$20.9099	$20.91	$20.90	$20.90
7 purchase totals =	$621.87		$672.9602	$672.97	$672.95	$672.90