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	$18.44	4.478%	$19.2657	$19.27	$19.25	$19.30
Purchase #2	$205.61	7.821%	$221.6908	$221.69	$221.70	$221.70
Purchase #3	$33.98	6.415%	$36.1598	$36.16	$36.15	$36.20
Purchase #4	$29.42	12.512%	$33.101	$33.10	$33.10	$33.10
Purchase #5	$62.96	5.110%	$66.1773	$66.18	$66.20	$66.20
Purchase #6	$18.66	9.858%	$20.4995	$20.50	$20.50	$20.50
Purchase #7	$233.32	3.862%	$242.3308	$242.33	$242.35	$242.30
7 purchase totals =	$602.39		$639.2249	$639.23	$639.25	$639.30