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	$115.25	13.479%	$130.7845	$130.78	$130.80	$130.80
Purchase #2	$54.86	4.353%	$57.2481	$57.25	$57.25	$57.20
Purchase #3	$179.26	4.390%	$187.1295	$187.13	$187.15	$187.10
Purchase #4	$51.46	3.825%	$53.4283	$53.43	$53.45	$53.40
Purchase #5	$38.87	3.654%	$40.2903	$40.29	$40.30	$40.30
Purchase #6	$96.50	10.715%	$106.84	$106.84	$106.85	$106.80
Purchase #7	$60.37	8.105%	$65.263	$65.26	$65.25	$65.30
7 purchase totals =	$596.57		$640.9837	$640.98	$641.05	$640.90