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	$99.88	11.652%	$111.518	$111.52	$111.50	$111.50
Purchase #2	$190.64	4.600%	$199.4094	$199.41	$199.40	$199.40
Purchase #3	$10.72	8.379%	$11.6182	$11.62	$11.60	$11.60
Purchase #4	$76.79	13.116%	$86.8618	$86.86	$86.85	$86.90
Purchase #5	$25.68	10.553%	$28.39	$28.39	$28.40	$28.40
Purchase #6	$250.86	13.641%	$285.0798	$285.08	$285.10	$285.10
Purchase #7	$99.25	4.627%	$103.8423	$103.84	$103.85	$103.80
7 purchase totals =	$753.82		$826.7195	$826.72	$826.70	$826.70