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	$12.90	3.114%	$13.3017	$13.30	$13.30	$13.30
Purchase #2	$45.49	4.303%	$47.4474	$47.45	$47.45	$47.40
Purchase #3	$160.29	7.687%	$172.6115	$172.61	$172.60	$172.60
Purchase #4	$135.50	6.754%	$144.6517	$144.65	$144.65	$144.70
Purchase #5	$37.46	6.777%	$39.9987	$40.00	$40.00	$40.00
Purchase #6	$176.97	7.410%	$190.0835	$190.08	$190.10	$190.10
Purchase #7	$173.63	6.229%	$184.4454	$184.45	$184.45	$184.40
7 purchase totals =	$742.24		$792.5399	$792.54	$792.55	$792.50