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	$79.54	13.448%	$90.2365	$90.24	$90.25	$90.20
Purchase #2	$167.81	6.797%	$179.216	$179.22	$179.20	$179.20
Purchase #3	$9.29	12.492%	$10.4505	$10.45	$10.45	$10.50
Purchase #4	$80.48	3.608%	$83.3837	$83.38	$83.40	$83.40
Purchase #5	$247.85	4.387%	$258.7232	$258.72	$258.70	$258.70
Purchase #6	$232.79	3.148%	$240.1182	$240.12	$240.10	$240.10
Purchase #7	$166.85	5.451%	$175.945	$175.95	$175.95	$175.90
7 purchase totals =	$984.61		$1,038.0731	$1,038.08	$1,038.05	$1,038.00