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	$111.53	10.541%	$123.2864	$123.29	$123.30	$123.30
Purchase #2	$249.55	7.174%	$267.4527	$267.45	$267.45	$267.50
Purchase #3	$74.72	4.606%	$78.1616	$78.16	$78.15	$78.20
Purchase #4	$120.35	11.512%	$134.2047	$134.20	$134.20	$134.20
Purchase #5	$120.97	5.147%	$127.1963	$127.20	$127.20	$127.20
Purchase #6	$131.65	3.849%	$136.7172	$136.72	$136.70	$136.70
Purchase #7	$117.51	10.745%	$130.1364	$130.14	$130.15	$130.10
7 purchase totals =	$926.28		$997.1553	$997.16	$997.15	$997.20