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	$16.31	3.747%	$16.9211	$16.92	$16.90	$16.90
Purchase #2	$171.30	4.532%	$179.0633	$179.06	$179.05	$179.10
Purchase #3	$140.87	7.301%	$151.1549	$151.15	$151.15	$151.20
Purchase #4	$54.83	12.648%	$61.7649	$61.76	$61.75	$61.80
Purchase #5	$130.67	12.452%	$146.941	$146.94	$146.95	$146.90
Purchase #6	$143.91	10.752%	$159.3832	$159.38	$159.40	$159.40
Purchase #7	$34.80	8.307%	$37.6908	$37.69	$37.70	$37.70
7 purchase totals =	$692.69		$752.9192	$752.90	$752.90	$753.00