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	$165.72	9.787%	$181.939	$181.94	$181.95	$181.90
Purchase #2	$145.98	10.171%	$160.8276	$160.83	$160.85	$160.80
Purchase #3	$99.59	11.555%	$111.0976	$111.10	$111.10	$111.10
Purchase #4	$42.55	11.322%	$47.3675	$47.37	$47.35	$47.40
Purchase #5	$24.77	6.433%	$26.3635	$26.36	$26.35	$26.40
Purchase #6	$66.83	11.370%	$74.4286	$74.43	$74.45	$74.40
Purchase #7	$92.82	11.239%	$103.252	$103.25	$103.25	$103.30
7 purchase totals =	$638.26		$705.2758	$705.28	$705.30	$705.30