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	$155.52	9.363%	$170.0813	$170.08	$170.10	$170.10
Purchase #2	$214.97	8.444%	$233.1221	$233.12	$233.10	$233.10
Purchase #3	$183.64	11.573%	$204.8927	$204.89	$204.90	$204.90
Purchase #4	$43.84	3.342%	$45.3051	$45.31	$45.30	$45.30
Purchase #5	$149.55	13.794%	$170.1789	$170.18	$170.20	$170.20
Purchase #6	$39.33	9.281%	$42.9802	$42.98	$43.00	$43.00
Purchase #7	$53.71	11.468%	$59.8695	$59.87	$59.85	$59.90
7 purchase totals =	$840.56		$926.4298	$926.43	$926.45	$926.50