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	$44.58	13.213%	$50.4704	$50.47	$50.45	$50.50
Purchase #2	$116.94	8.720%	$127.1372	$127.14	$127.15	$127.10
Purchase #3	$77.94	6.249%	$82.8105	$82.81	$82.80	$82.80
Purchase #4	$39.27	8.162%	$42.4752	$42.48	$42.50	$42.50
Purchase #5	$168.47	9.525%	$184.5168	$184.52	$184.50	$184.50
Purchase #6	$174.29	12.278%	$195.6893	$195.69	$195.70	$195.70
Purchase #7	$145.61	5.354%	$153.406	$153.41	$153.40	$153.40
7 purchase totals =	$767.10		$836.5054	$836.52	$836.50	$836.50