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	$178.41	6.720%	$190.3992	$190.40	$190.40	$190.40
Purchase #2	$67.36	5.206%	$70.8668	$70.87	$70.85	$70.90
Purchase #3	$222.57	11.766%	$248.7576	$248.76	$248.75	$248.80
Purchase #4	$85.96	3.732%	$89.168	$89.17	$89.15	$89.20
Purchase #5	$10.39	6.734%	$11.0897	$11.09	$11.10	$11.10
Purchase #6	$121.89	10.261%	$134.3971	$134.40	$134.40	$134.40
Purchase #7	$158.84	5.399%	$167.4158	$167.42	$167.40	$167.40
7 purchase totals =	$845.42		$912.0942	$912.11	$912.05	$912.20