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	$38.40	11.711%	$42.897	$42.90	$42.90	$42.90
Purchase #2	$91.57	9.540%	$100.3058	$100.31	$100.30	$100.30
Purchase #3	$48.76	9.118%	$53.2059	$53.21	$53.20	$53.20
Purchase #4	$52.72	4.195%	$54.9316	$54.93	$54.95	$54.90
Purchase #5	$40.81	6.631%	$43.5161	$43.52	$43.50	$43.50
Purchase #6	$56.41	12.792%	$63.626	$63.63	$63.65	$63.60
Purchase #7	$163.91	4.792%	$171.7646	$171.76	$171.75	$171.80
7 purchase totals =	$492.58		$530.2470	$530.26	$530.25	$530.20