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	$26.79	6.755%	$28.5997	$28.60	$28.60	$28.60
Purchase #2	$25.25	7.848%	$27.2316	$27.23	$27.25	$27.20
Purchase #3	$107.82	8.794%	$117.3017	$117.30	$117.30	$117.30
Purchase #4	$48.28	10.760%	$53.4749	$53.47	$53.45	$53.50
Purchase #5	$34.58	11.584%	$38.5857	$38.59	$38.60	$38.60
Purchase #6	$201.94	4.277%	$210.577	$210.58	$210.60	$210.60
Purchase #7	$71.77	7.456%	$77.1212	$77.12	$77.10	$77.10
7 purchase totals =	$516.43		$552.8918	$552.89	$552.90	$552.90