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	$66.69	8.344%	$72.2546	$72.25	$72.25	$72.30
Purchase #2	$116.47	9.117%	$127.0886	$127.09	$127.10	$127.10
Purchase #3	$109.94	6.313%	$116.8805	$116.88	$116.90	$116.90
Purchase #4	$211.63	8.828%	$230.3127	$230.31	$230.30	$230.30
Purchase #5	$7.26	4.857%	$7.6126	$7.61	$7.60	$7.60
Purchase #6	$52.73	9.276%	$57.6212	$57.62	$57.60	$57.60
Purchase #7	$27.32	7.729%	$29.4316	$29.43	$29.45	$29.40
7 purchase totals =	$592.04		$641.2018	$641.19	$641.20	$641.20