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	$28.32	5.609%	$29.9085	$29.91	$29.90	$29.90
Purchase #2	$172.93	13.375%	$196.0594	$196.06	$196.05	$196.10
Purchase #3	$111.59	11.838%	$124.8	$124.80	$124.80	$124.80
Purchase #4	$173.52	6.172%	$184.2297	$184.23	$184.25	$184.20
Purchase #5	$25.77	3.349%	$26.633	$26.63	$26.65	$26.60
Purchase #6	$246.66	7.847%	$266.0154	$266.02	$266.00	$266.00
Purchase #7	$148.90	3.159%	$153.6038	$153.60	$153.60	$153.60
7 purchase totals =	$907.69		$981.2498	$981.25	$981.25	$981.20