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	$9.74	5.127%	$10.2394	$10.24	$10.25	$10.20
Purchase #2	$145.61	10.408%	$160.7651	$160.77	$160.75	$160.80
Purchase #3	$137.59	13.773%	$156.5403	$156.54	$156.55	$156.50
Purchase #4	$153.29	4.651%	$160.4195	$160.42	$160.40	$160.40
Purchase #5	$95.79	13.150%	$108.3864	$108.39	$108.40	$108.40
Purchase #6	$30.79	4.167%	$32.073	$32.07	$32.05	$32.10
Purchase #7	$178.27	7.756%	$192.0966	$192.10	$192.10	$192.10
7 purchase totals =	$751.08		$820.5203	$820.53	$820.50	$820.50