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	$63.56	10.341%	$70.1327	$70.13	$70.15	$70.10
Purchase #2	$175.79	8.600%	$190.9079	$190.91	$190.90	$190.90
Purchase #3	$47.58	7.245%	$51.0272	$51.03	$51.05	$51.00
Purchase #4	$201.57	6.423%	$214.5168	$214.52	$214.50	$214.50
Purchase #5	$39.37	3.143%	$40.6074	$40.61	$40.60	$40.60
Purchase #6	$167.63	13.394%	$190.0824	$190.08	$190.10	$190.10
Purchase #7	$97.74	6.114%	$103.7158	$103.72	$103.70	$103.70
7 purchase totals =	$793.24		$860.9902	$861.00	$861.00	$860.90