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	$98.42	5.123%	$103.4621	$103.46	$103.45	$103.50
Purchase #2	$143.92	11.427%	$160.3657	$160.37	$160.35	$160.40
Purchase #3	$149.57	8.346%	$162.0531	$162.05	$162.05	$162.10
Purchase #4	$97.71	10.444%	$107.9148	$107.91	$107.90	$107.90
Purchase #5	$185.47	10.705%	$205.3246	$205.32	$205.30	$205.30
Purchase #6	$85.58	5.381%	$90.1851	$90.19	$90.20	$90.20
Purchase #7	$48.91	5.492%	$51.5961	$51.60	$51.60	$51.60
7 purchase totals =	$809.58		$880.9015	$880.90	$880.85	$881.00