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	$229.92	13.684%	$261.3823	$261.38	$261.40	$261.40
Purchase #2	$183.95	8.464%	$199.5195	$199.52	$199.50	$199.50
Purchase #3	$11.86	5.134%	$12.4689	$12.47	$12.45	$12.50
Purchase #4	$160.60	7.404%	$172.4908	$172.49	$172.50	$172.50
Purchase #5	$77.89	13.287%	$88.2392	$88.24	$88.25	$88.20
Purchase #6	$55.90	4.815%	$58.5916	$58.59	$58.60	$58.60
Purchase #7	$91.51	6.852%	$97.7803	$97.78	$97.80	$97.80
7 purchase totals =	$811.63		$890.4726	$890.47	$890.50	$890.50