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	$11.32	12.305%	$12.7129	$12.71	$12.70	$12.70
Purchase #2	$147.83	4.670%	$154.7337	$154.73	$154.75	$154.70
Purchase #3	$46.43	12.575%	$52.2686	$52.27	$52.25	$52.30
Purchase #4	$58.75	13.477%	$66.6677	$66.67	$66.65	$66.70
Purchase #5	$43.27	6.157%	$45.9341	$45.93	$45.95	$45.90
Purchase #6	$65.44	3.364%	$67.6414	$67.64	$67.65	$67.60
Purchase #7	$33.75	10.242%	$37.2067	$37.21	$37.20	$37.20
7 purchase totals =	$406.79		$437.1651	$437.16	$437.15	$437.10