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	$203.64	6.868%	$217.626	$217.63	$217.65	$217.60
Purchase #2	$207.88	6.709%	$221.8267	$221.83	$221.85	$221.80
Purchase #3	$139.90	7.768%	$150.7674	$150.77	$150.75	$150.80
Purchase #4	$99.86	11.439%	$111.283	$111.28	$111.30	$111.30
Purchase #5	$135.96	10.638%	$150.4234	$150.42	$150.40	$150.40
Purchase #6	$47.50	3.375%	$49.1031	$49.10	$49.10	$49.10
Purchase #7	$98.32	3.139%	$101.4063	$101.41	$101.40	$101.40
7 purchase totals =	$933.06		$1,002.4359	$1,002.44	$1,002.45	$1,002.40