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	$226.40	13.637%	$257.2742	$257.27	$257.25	$257.30
Purchase #2	$149.96	12.595%	$168.8475	$168.85	$168.85	$168.80
Purchase #3	$100.31	11.555%	$111.9008	$111.90	$111.90	$111.90
Purchase #4	$129.48	9.142%	$141.3171	$141.32	$141.30	$141.30
Purchase #5	$42.85	9.382%	$46.8702	$46.87	$46.85	$46.90
Purchase #6	$18.74	7.774%	$20.1968	$20.20	$20.20	$20.20
Purchase #7	$10.87	11.195%	$12.0869	$12.09	$12.10	$12.10
7 purchase totals =	$678.61		$758.4935	$758.50	$758.45	$758.50