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	$36.75	9.513%	$40.246	$40.25	$40.25	$40.20
Purchase #2	$87.95	8.104%	$95.0775	$95.08	$95.10	$95.10
Purchase #3	$77.84	9.827%	$85.4893	$85.49	$85.50	$85.50
Purchase #4	$170.31	12.590%	$191.752	$191.75	$191.75	$191.80
Purchase #5	$213.74	7.557%	$229.8923	$229.89	$229.90	$229.90
Purchase #6	$44.26	12.463%	$49.7761	$49.78	$49.80	$49.80
Purchase #7	$152.67	12.866%	$172.3125	$172.31	$172.30	$172.30
7 purchase totals =	$783.52		$864.5457	$864.55	$864.60	$864.60