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	$107.33	7.616%	$115.5043	$115.50	$115.50	$115.50
Purchase #2	$51.39	5.327%	$54.1275	$54.13	$54.15	$54.10
Purchase #3	$9.98	10.453%	$11.0232	$11.02	$11.00	$11.00
Purchase #4	$243.81	12.761%	$274.9226	$274.92	$274.90	$274.90
Purchase #5	$112.51	3.575%	$116.5322	$116.53	$116.55	$116.50
Purchase #6	$248.78	6.443%	$264.8089	$264.81	$264.80	$264.80
Purchase #7	$18.38	7.114%	$19.6876	$19.69	$19.70	$19.70
7 purchase totals =	$792.18		$856.6063	$856.60	$856.60	$856.50