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	$73.47	7.306%	$78.8377	$78.84	$78.85	$78.80
Purchase #2	$235.66	9.504%	$258.0571	$258.06	$258.05	$258.10
Purchase #3	$82.95	13.830%	$94.422	$94.42	$94.40	$94.40
Purchase #4	$214.69	8.381%	$232.6832	$232.68	$232.70	$232.70
Purchase #5	$29.37	10.548%	$32.4679	$32.47	$32.45	$32.50
Purchase #6	$245.86	12.658%	$276.981	$276.98	$277.00	$277.00
Purchase #7	$139.71	10.144%	$153.8822	$153.88	$153.90	$153.90
7 purchase totals =	$1,021.71		$1,127.3311	$1,127.33	$1,127.35	$1,127.40