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	$89.80	10.604%	$99.3224	$99.32	$99.30	$99.30
Purchase #2	$19.38	13.220%	$21.942	$21.94	$21.95	$21.90
Purchase #3	$203.27	6.857%	$217.2082	$217.21	$217.20	$217.20
Purchase #4	$40.29	13.687%	$45.8045	$45.80	$45.80	$45.80
Purchase #5	$134.43	13.796%	$152.976	$152.98	$153.00	$153.00
Purchase #6	$250.47	4.763%	$262.3999	$262.40	$262.40	$262.40
Purchase #7	$82.96	10.537%	$91.7015	$91.70	$91.70	$91.70
7 purchase totals =	$820.60		$891.3545	$891.35	$891.35	$891.30