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	$12.98	3.808%	$13.4743	$13.47	$13.45	$13.50
Purchase #2	$175.29	8.234%	$189.7234	$189.72	$189.70	$189.70
Purchase #3	$136.33	7.134%	$146.0558	$146.06	$146.05	$146.10
Purchase #4	$81.50	11.174%	$90.6068	$90.61	$90.60	$90.60
Purchase #5	$37.32	8.341%	$40.4329	$40.43	$40.45	$40.40
Purchase #6	$190.89	13.314%	$216.3051	$216.31	$216.30	$216.30
Purchase #7	$56.85	5.581%	$60.0228	$60.02	$60.00	$60.00
7 purchase totals =	$691.16		$756.6211	$756.62	$756.55	$756.60