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	$213.74	6.274%	$227.15	$227.15	$227.15	$227.20
Purchase #2	$147.77	10.103%	$162.6992	$162.70	$162.70	$162.70
Purchase #3	$30.39	13.146%	$34.3851	$34.39	$34.40	$34.40
Purchase #4	$31.72	10.342%	$35.0005	$35.00	$35.00	$35.00
Purchase #5	$33.73	4.579%	$35.2745	$35.27	$35.25	$35.30
Purchase #6	$229.40	8.749%	$249.4702	$249.47	$249.45	$249.50
Purchase #7	$78.64	9.205%	$85.8788	$85.88	$85.90	$85.90
7 purchase totals =	$765.39		$829.8583	$829.86	$829.85	$830.00