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	$145.93	8.674%	$158.588	$158.59	$158.60	$158.60
Purchase #2	$117.40	4.286%	$122.4318	$122.43	$122.45	$122.40
Purchase #3	$18.61	11.499%	$20.75	$20.75	$20.75	$20.80
Purchase #4	$83.35	11.413%	$92.8627	$92.86	$92.85	$92.90
Purchase #5	$47.95	13.541%	$54.4429	$54.44	$54.45	$54.40
Purchase #6	$208.44	3.590%	$215.923	$215.92	$215.90	$215.90
Purchase #7	$168.82	13.214%	$191.1279	$191.13	$191.15	$191.10
7 purchase totals =	$790.50		$856.1263	$856.12	$856.15	$856.10