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	$62.88	7.381%	$67.5212	$67.52	$67.50	$67.50
Purchase #2	$145.63	11.473%	$162.3381	$162.34	$162.35	$162.30
Purchase #3	$221.54	10.554%	$244.9213	$244.92	$244.90	$244.90
Purchase #4	$167.28	3.370%	$172.9173	$172.92	$172.90	$172.90
Purchase #5	$174.37	10.693%	$193.0154	$193.02	$193.00	$193.00
Purchase #6	$111.90	12.293%	$125.6559	$125.66	$125.65	$125.70
Purchase #7	$11.73	6.510%	$12.4936	$12.49	$12.50	$12.50
7 purchase totals =	$895.33		$978.8628	$978.87	$978.80	$978.80