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	$53.72	11.477%	$59.8854	$59.89	$59.90	$59.90
Purchase #2	$48.92	7.494%	$52.5861	$52.59	$52.60	$52.60
Purchase #3	$56.77	6.105%	$60.2358	$60.24	$60.25	$60.20
Purchase #4	$10.44	3.268%	$10.7812	$10.78	$10.80	$10.80
Purchase #5	$57.31	6.324%	$60.9343	$60.93	$60.95	$60.90
Purchase #6	$208.84	9.804%	$229.3147	$229.31	$229.30	$229.30
Purchase #7	$22.45	8.126%	$24.2743	$24.27	$24.25	$24.30
7 purchase totals =	$458.45		$498.0118	$498.01	$498.05	$498.00