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	$235.98	8.406%	$255.8165	$255.82	$255.80	$255.80
Purchase #2	$91.98	9.189%	$100.432	$100.43	$100.45	$100.40
Purchase #3	$45.64	10.741%	$50.5422	$50.54	$50.55	$50.50
Purchase #4	$5.92	7.321%	$6.3534	$6.35	$6.35	$6.40
Purchase #5	$87.41	12.241%	$98.1099	$98.11	$98.10	$98.10
Purchase #6	$82.51	12.461%	$92.7916	$92.79	$92.80	$92.80
Purchase #7	$44.91	10.465%	$49.6098	$49.61	$49.60	$49.60
7 purchase totals =	$594.35		$653.6554	$653.65	$653.65	$653.60