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	$245.94	11.110%	$273.2639	$273.26	$273.25	$273.30
Purchase #2	$153.86	3.833%	$159.7575	$159.76	$159.75	$159.80
Purchase #3	$6.43	10.188%	$7.0851	$7.09	$7.10	$7.10
Purchase #4	$77.92	5.142%	$81.9266	$81.93	$81.95	$81.90
Purchase #5	$146.30	4.763%	$153.2683	$153.27	$153.25	$153.30
Purchase #6	$151.41	10.605%	$167.467	$167.47	$167.45	$167.50
Purchase #7	$212.27	12.154%	$238.0693	$238.07	$238.05	$238.10
7 purchase totals =	$994.13		$1,080.8377	$1,080.85	$1,080.80	$1,081.00