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	$57.70	3.833%	$59.9116	$59.91	$59.90	$59.90
Purchase #2	$248.97	6.467%	$265.0709	$265.07	$265.05	$265.10
Purchase #3	$242.58	5.585%	$256.1281	$256.13	$256.15	$256.10
Purchase #4	$177.34	12.121%	$198.8354	$198.84	$198.85	$198.80
Purchase #5	$103.59	7.822%	$111.6928	$111.69	$111.70	$111.70
Purchase #6	$20.70	8.421%	$22.4431	$22.44	$22.45	$22.40
Purchase #7	$19.52	10.741%	$21.6166	$21.62	$21.60	$21.60
7 purchase totals =	$870.40		$935.6985	$935.70	$935.70	$935.60