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	$22.72	7.783%	$24.4883	$24.49	$24.50	$24.50
Purchase #2	$160.41	9.755%	$176.058	$176.06	$176.05	$176.10
Purchase #3	$105.76	11.699%	$118.1329	$118.13	$118.15	$118.10
Purchase #4	$147.29	12.191%	$165.2461	$165.25	$165.25	$165.20
Purchase #5	$180.76	10.148%	$199.1035	$199.10	$199.10	$199.10
Purchase #6	$37.48	13.304%	$42.4663	$42.47	$42.45	$42.50
Purchase #7	$156.67	3.606%	$162.3195	$162.32	$162.30	$162.30
7 purchase totals =	$811.09		$887.8146	$887.82	$887.80	$887.80