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	$120.65	13.332%	$136.7351	$136.74	$136.75	$136.70
Purchase #2	$60.50	3.548%	$62.6465	$62.65	$62.65	$62.60
Purchase #3	$58.34	11.523%	$65.0625	$65.06	$65.05	$65.10
Purchase #4	$85.64	4.590%	$89.5709	$89.57	$89.55	$89.60
Purchase #5	$85.80	3.279%	$88.6134	$88.61	$88.60	$88.60
Purchase #6	$146.60	5.763%	$155.0486	$155.05	$155.05	$155.00
Purchase #7	$74.69	12.240%	$83.8321	$83.83	$83.85	$83.80
7 purchase totals =	$632.22		$681.5091	$681.51	$681.50	$681.40