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	$186.74	6.840%	$199.513	$199.51	$199.50	$199.50
Purchase #2	$206.83	6.670%	$220.6256	$220.63	$220.65	$220.60
Purchase #3	$211.84	12.589%	$238.5085	$238.51	$238.50	$238.50
Purchase #4	$49.26	12.643%	$55.4879	$55.49	$55.50	$55.50
Purchase #5	$114.30	11.560%	$127.5131	$127.51	$127.50	$127.50
Purchase #6	$37.93	12.656%	$42.7304	$42.73	$42.75	$42.70
Purchase #7	$69.96	10.566%	$77.352	$77.35	$77.35	$77.40
7 purchase totals =	$876.86		$961.7305	$961.73	$961.75	$961.70