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	$220.56	13.567%	$250.4834	$250.48	$250.50	$250.50
Purchase #2	$90.32	9.774%	$99.1479	$99.15	$99.15	$99.10
Purchase #3	$68.93	12.110%	$77.2774	$77.28	$77.30	$77.30
Purchase #4	$250.85	6.318%	$266.6987	$266.70	$266.70	$266.70
Purchase #5	$103.79	7.337%	$111.4051	$111.41	$111.40	$111.40
Purchase #6	$173.98	11.666%	$194.2765	$194.28	$194.30	$194.30
Purchase #7	$140.50	8.518%	$152.4678	$152.47	$152.45	$152.50
7 purchase totals =	$1,048.93		$1,151.7568	$1,151.77	$1,151.80	$1,151.80