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	$89.30	11.605%	$99.6633	$99.66	$99.65	$99.70
Purchase #2	$115.75	9.818%	$127.1143	$127.11	$127.10	$127.10
Purchase #3	$132.94	3.585%	$137.7059	$137.71	$137.70	$137.70
Purchase #4	$17.39	13.477%	$19.7337	$19.73	$19.75	$19.70
Purchase #5	$142.29	3.159%	$146.7849	$146.78	$146.80	$146.80
Purchase #6	$44.98	7.125%	$48.1848	$48.18	$48.20	$48.20
Purchase #7	$77.89	11.787%	$87.0709	$87.07	$87.05	$87.10
7 purchase totals =	$620.54		$666.2578	$666.24	$666.25	$666.30