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	$165.72	7.591%	$178.2998	$178.30	$178.30	$178.30
Purchase #2	$173.65	10.285%	$191.5099	$191.51	$191.50	$191.50
Purchase #3	$8.66	13.128%	$9.7969	$9.80	$9.80	$9.80
Purchase #4	$137.28	10.348%	$151.4857	$151.49	$151.50	$151.50
Purchase #5	$142.53	5.131%	$149.8432	$149.84	$149.85	$149.80
Purchase #6	$216.90	3.224%	$223.8929	$223.89	$223.90	$223.90
Purchase #7	$49.80	10.554%	$55.0559	$55.06	$55.05	$55.10
7 purchase totals =	$894.54		$959.8843	$959.89	$959.90	$959.90