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	$200.92	4.567%	$210.096	$210.10	$210.10	$210.10
Purchase #2	$210.35	13.294%	$238.3139	$238.31	$238.30	$238.30
Purchase #3	$174.56	8.224%	$188.9158	$188.92	$188.90	$188.90
Purchase #4	$183.89	13.606%	$208.9101	$208.91	$208.90	$208.90
Purchase #5	$78.90	7.850%	$85.0937	$85.09	$85.10	$85.10
Purchase #6	$118.31	4.655%	$123.8173	$123.82	$123.80	$123.80
Purchase #7	$239.85	5.318%	$252.6052	$252.61	$252.60	$252.60
7 purchase totals =	$1,206.78		$1,307.7520	$1,307.76	$1,307.70	$1,307.70