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	$149.73	6.419%	$159.3412	$159.34	$159.35	$159.30
Purchase #2	$47.85	9.119%	$52.2134	$52.21	$52.20	$52.20
Purchase #3	$91.27	10.473%	$100.8287	$100.83	$100.85	$100.80
Purchase #4	$8.29	5.196%	$8.7207	$8.72	$8.70	$8.70
Purchase #5	$117.73	7.503%	$126.5633	$126.56	$126.55	$126.60
Purchase #6	$100.74	4.493%	$105.2662	$105.27	$105.25	$105.30
Purchase #7	$46.62	7.777%	$50.2456	$50.25	$50.25	$50.20
7 purchase totals =	$562.23		$603.1791	$603.18	$603.15	$603.10