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	$54.74	3.372%	$56.5858	$56.59	$56.60	$56.60
Purchase #2	$79.46	13.618%	$90.2809	$90.28	$90.30	$90.30
Purchase #3	$111.99	11.363%	$124.7154	$124.72	$124.70	$124.70
Purchase #4	$50.85	7.509%	$54.6683	$54.67	$54.65	$54.70
Purchase #5	$236.58	11.714%	$264.293	$264.29	$264.30	$264.30
Purchase #6	$37.94	11.818%	$42.4237	$42.42	$42.40	$42.40
Purchase #7	$202.66	11.607%	$226.1827	$226.18	$226.20	$226.20
7 purchase totals =	$774.22		$859.1498	$859.15	$859.15	$859.20