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	$40.28	9.532%	$44.1195	$44.12	$44.10	$44.10
Purchase #2	$134.47	11.553%	$150.0053	$150.01	$150.00	$150.00
Purchase #3	$231.28	10.351%	$255.2198	$255.22	$255.20	$255.20
Purchase #4	$152.79	9.601%	$167.4594	$167.46	$167.45	$167.50
Purchase #5	$33.87	10.117%	$37.2966	$37.30	$37.30	$37.30
Purchase #6	$173.58	9.415%	$189.9226	$189.92	$189.90	$189.90
Purchase #7	$223.39	13.445%	$253.4248	$253.42	$253.40	$253.40
7 purchase totals =	$989.66		$1,097.4480	$1,097.45	$1,097.35	$1,097.40