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	$61.84	13.770%	$70.3554	$70.36	$70.35	$70.40
Purchase #2	$28.25	4.374%	$29.4857	$29.49	$29.50	$29.50
Purchase #3	$152.76	12.265%	$171.496	$171.50	$171.50	$171.50
Purchase #4	$105.48	5.627%	$111.4154	$111.42	$111.40	$111.40
Purchase #5	$157.41	6.189%	$167.1521	$167.15	$167.15	$167.20
Purchase #6	$116.50	8.225%	$126.0821	$126.08	$126.10	$126.10
Purchase #7	$160.66	8.751%	$174.7194	$174.72	$174.70	$174.70
7 purchase totals =	$782.90		$850.7061	$850.72	$850.70	$850.80