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	$148.45	12.391%	$166.8444	$166.84	$166.85	$166.80
Purchase #2	$108.78	10.409%	$120.1029	$120.10	$120.10	$120.10
Purchase #3	$231.64	10.703%	$256.4324	$256.43	$256.45	$256.40
Purchase #4	$62.45	13.302%	$70.7571	$70.76	$70.75	$70.80
Purchase #5	$90.99	12.231%	$102.119	$102.12	$102.10	$102.10
Purchase #6	$154.52	3.224%	$159.5017	$159.50	$159.50	$159.50
Purchase #7	$226.26	4.376%	$236.1611	$236.16	$236.15	$236.20
7 purchase totals =	$1,023.09		$1,111.9186	$1,111.91	$1,111.90	$1,111.90