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	$138.93	13.838%	$158.1551	$158.16	$158.15	$158.20
Purchase #2	$122.89	10.661%	$135.9913	$135.99	$136.00	$136.00
Purchase #3	$93.86	10.703%	$103.9058	$103.91	$103.90	$103.90
Purchase #4	$72.60	13.530%	$82.4228	$82.42	$82.40	$82.40
Purchase #5	$170.89	8.312%	$185.0944	$185.09	$185.10	$185.10
Purchase #6	$169.43	11.113%	$188.2588	$188.26	$188.25	$188.30
Purchase #7	$107.29	10.599%	$118.6617	$118.66	$118.65	$118.70
7 purchase totals =	$875.89		$972.4899	$972.49	$972.45	$972.60