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	$10.55	11.455%	$11.7585	$11.76	$11.75	$11.80
Purchase #2	$114.40	13.540%	$129.8898	$129.89	$129.90	$129.90
Purchase #3	$61.37	6.323%	$65.2504	$65.25	$65.25	$65.30
Purchase #4	$93.44	13.551%	$106.1021	$106.10	$106.10	$106.10
Purchase #5	$153.91	6.617%	$164.0942	$164.09	$164.10	$164.10
Purchase #6	$99.31	6.308%	$105.5745	$105.57	$105.55	$105.60
Purchase #7	$50.77	7.155%	$54.4026	$54.40	$54.40	$54.40
7 purchase totals =	$583.75		$637.0721	$637.06	$637.05	$637.20