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	$137.47	9.569%	$150.6245	$150.62	$150.60	$150.60
Purchase #2	$218.66	10.104%	$240.7534	$240.75	$240.75	$240.80
Purchase #3	$72.93	9.545%	$79.8912	$79.89	$79.90	$79.90
Purchase #4	$82.39	10.568%	$91.097	$91.10	$91.10	$91.10
Purchase #5	$20.44	4.710%	$21.4027	$21.40	$21.40	$21.40
Purchase #6	$60.68	13.485%	$68.8627	$68.86	$68.85	$68.90
Purchase #7	$86.91	3.841%	$90.2482	$90.25	$90.25	$90.20
7 purchase totals =	$679.48		$742.8797	$742.87	$742.85	$742.90