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	$248.31	12.413%	$279.1327	$279.13	$279.15	$279.10
Purchase #2	$20.62	5.433%	$21.7403	$21.74	$21.75	$21.70
Purchase #3	$71.56	3.358%	$73.963	$73.96	$73.95	$74.00
Purchase #4	$34.62	7.261%	$37.1338	$37.13	$37.15	$37.10
Purchase #5	$38.49	6.840%	$41.1227	$41.12	$41.10	$41.10
Purchase #6	$18.93	10.613%	$20.939	$20.94	$20.95	$20.90
Purchase #7	$233.75	9.185%	$255.2199	$255.22	$255.20	$255.20
7 purchase totals =	$666.28		$729.2514	$729.24	$729.25	$729.10