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	$170.89	10.632%	$189.059	$189.06	$189.05	$189.10
Purchase #2	$32.54	8.827%	$35.4123	$35.41	$35.40	$35.40
Purchase #3	$58.80	13.500%	$66.738	$66.74	$66.75	$66.70
Purchase #4	$123.41	8.122%	$133.4334	$133.43	$133.45	$133.40
Purchase #5	$184.31	8.669%	$200.2878	$200.29	$200.30	$200.30
Purchase #6	$54.73	8.198%	$59.2168	$59.22	$59.20	$59.20
Purchase #7	$45.69	10.627%	$50.5455	$50.55	$50.55	$50.50
7 purchase totals =	$670.37		$734.6928	$734.70	$734.70	$734.60