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	$103.49	6.571%	$110.2903	$110.29	$110.30	$110.30
Purchase #2	$192.75	11.107%	$214.1587	$214.16	$214.15	$214.20
Purchase #3	$36.38	13.327%	$41.2284	$41.23	$41.25	$41.20
Purchase #4	$97.77	7.526%	$105.1282	$105.13	$105.15	$105.10
Purchase #5	$155.59	5.763%	$164.5567	$164.56	$164.55	$164.60
Purchase #6	$49.50	12.335%	$55.6058	$55.61	$55.60	$55.60
Purchase #7	$141.27	4.821%	$148.0806	$148.08	$148.10	$148.10
7 purchase totals =	$776.75		$839.0487	$839.06	$839.10	$839.10