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	$40.50	4.380%	$42.2739	$42.27	$42.25	$42.30
Purchase #2	$14.45	8.136%	$15.6257	$15.63	$15.65	$15.60
Purchase #3	$172.49	6.609%	$183.8899	$183.89	$183.90	$183.90
Purchase #4	$61.60	9.537%	$67.4748	$67.47	$67.45	$67.50
Purchase #5	$229.64	8.133%	$248.3166	$248.32	$248.30	$248.30
Purchase #6	$58.74	9.210%	$64.15	$64.15	$64.15	$64.20
Purchase #7	$247.27	5.205%	$260.1404	$260.14	$260.15	$260.10
7 purchase totals =	$824.69		$881.8713	$881.87	$881.85	$881.90