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	$228.59	12.484%	$257.1272	$257.13	$257.15	$257.10
Purchase #2	$174.29	10.420%	$192.451	$192.45	$192.45	$192.50
Purchase #3	$235.31	8.381%	$255.0313	$255.03	$255.05	$255.00
Purchase #4	$173.59	3.199%	$179.1431	$179.14	$179.15	$179.10
Purchase #5	$200.72	7.278%	$215.3284	$215.33	$215.35	$215.30
Purchase #6	$142.92	6.414%	$152.0869	$152.09	$152.10	$152.10
Purchase #7	$58.69	4.654%	$61.4214	$61.42	$61.40	$61.40
7 purchase totals =	$1,214.11		$1,312.5893	$1,312.59	$1,312.65	$1,312.50