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	$142.67	10.114%	$157.0996	$157.10	$157.10	$157.10
Purchase #2	$157.88	5.626%	$166.7623	$166.76	$166.75	$166.80
Purchase #3	$162.88	7.196%	$174.6008	$174.60	$174.60	$174.60
Purchase #4	$20.65	3.872%	$21.4496	$21.45	$21.45	$21.40
Purchase #5	$52.78	6.123%	$56.0117	$56.01	$56.00	$56.00
Purchase #6	$95.82	3.642%	$99.3098	$99.31	$99.30	$99.30
Purchase #7	$145.79	13.707%	$165.7734	$165.77	$165.75	$165.80
7 purchase totals =	$778.47		$841.0072	$841.00	$840.95	$841.00