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	$197.79	9.708%	$216.9915	$216.99	$217.00	$217.00
Purchase #2	$238.51	4.626%	$249.5435	$249.54	$249.55	$249.50
Purchase #3	$104.81	11.518%	$116.882	$116.88	$116.90	$116.90
Purchase #4	$67.31	9.614%	$73.7812	$73.78	$73.80	$73.80
Purchase #5	$29.88	10.131%	$32.9071	$32.91	$32.90	$32.90
Purchase #6	$34.28	13.497%	$38.9068	$38.91	$38.90	$38.90
Purchase #7	$104.26	7.304%	$111.8752	$111.88	$111.90	$111.90
7 purchase totals =	$776.84		$840.8873	$840.89	$840.95	$840.90