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	$131.52	8.836%	$143.1411	$143.14	$143.15	$143.10
Purchase #2	$72.50	11.191%	$80.6135	$80.61	$80.60	$80.60
Purchase #3	$108.35	13.405%	$122.8743	$122.87	$122.85	$122.90
Purchase #4	$146.61	4.753%	$153.5784	$153.58	$153.60	$153.60
Purchase #5	$174.54	4.158%	$181.7974	$181.80	$181.80	$181.80
Purchase #6	$32.38	10.835%	$35.8884	$35.89	$35.90	$35.90
Purchase #7	$170.98	6.102%	$181.4132	$181.41	$181.40	$181.40
7 purchase totals =	$836.88		$899.3063	$899.30	$899.30	$899.30