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	$92.84	7.726%	$100.0128	$100.01	$100.00	$100.00
Purchase #2	$18.74	9.196%	$20.4633	$20.46	$20.45	$20.50
Purchase #3	$206.49	10.709%	$228.603	$228.60	$228.60	$228.60
Purchase #4	$100.51	10.717%	$111.2817	$111.28	$111.30	$111.30
Purchase #5	$194.95	5.601%	$205.8691	$205.87	$205.85	$205.90
Purchase #6	$236.33	5.569%	$249.4912	$249.49	$249.50	$249.50
Purchase #7	$153.91	5.281%	$162.038	$162.04	$162.05	$162.00
7 purchase totals =	$1,003.77		$1,077.7591	$1,077.75	$1,077.75	$1,077.80