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	$135.78	6.541%	$144.6614	$144.66	$144.65	$144.70
Purchase #2	$196.43	12.421%	$220.8286	$220.83	$220.85	$220.80
Purchase #3	$173.95	4.801%	$182.3013	$182.30	$182.30	$182.30
Purchase #4	$60.31	12.205%	$67.6708	$67.67	$67.65	$67.70
Purchase #5	$49.63	9.753%	$54.4704	$54.47	$54.45	$54.50
Purchase #6	$83.75	10.596%	$92.6242	$92.62	$92.60	$92.60
Purchase #7	$49.89	5.716%	$52.7417	$52.74	$52.75	$52.70
7 purchase totals =	$749.74		$815.2984	$815.29	$815.25	$815.30