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	$77.33	6.713%	$82.5212	$82.52	$82.50	$82.50
Purchase #2	$151.28	6.217%	$160.6851	$160.69	$160.70	$160.70
Purchase #3	$42.70	9.248%	$46.6489	$46.65	$46.65	$46.60
Purchase #4	$125.97	5.265%	$132.6023	$132.60	$132.60	$132.60
Purchase #5	$57.91	13.571%	$65.769	$65.77	$65.75	$65.80
Purchase #6	$58.75	5.800%	$62.1575	$62.16	$62.15	$62.20
Purchase #7	$98.38	5.602%	$103.8912	$103.89	$103.90	$103.90
7 purchase totals =	$612.32		$654.2752	$654.28	$654.25	$654.30