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	$229.37	9.364%	$250.8482	$250.85	$250.85	$250.80
Purchase #2	$40.81	11.293%	$45.4187	$45.42	$45.40	$45.40
Purchase #3	$138.99	6.173%	$147.5699	$147.57	$147.55	$147.60
Purchase #4	$32.38	8.476%	$35.1245	$35.12	$35.10	$35.10
Purchase #5	$158.57	12.585%	$178.526	$178.53	$178.55	$178.50
Purchase #6	$143.60	5.643%	$151.7033	$151.70	$151.70	$151.70
Purchase #7	$60.56	12.183%	$67.938	$67.94	$67.95	$67.90
7 purchase totals =	$804.28		$877.1286	$877.13	$877.10	$877.00