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	$89.93	4.439%	$93.922	$93.92	$93.90	$93.90
Purchase #2	$159.71	3.853%	$165.8636	$165.86	$165.85	$165.90
Purchase #3	$77.41	3.361%	$80.0118	$80.01	$80.00	$80.00
Purchase #4	$42.38	6.574%	$45.1661	$45.17	$45.15	$45.20
Purchase #5	$132.47	6.839%	$141.5296	$141.53	$141.55	$141.50
Purchase #6	$137.63	8.307%	$149.0629	$149.06	$149.05	$149.10
Purchase #7	$87.67	3.722%	$90.9331	$90.93	$90.95	$90.90
7 purchase totals =	$727.20		$766.4891	$766.48	$766.45	$766.50