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	$13.30	4.685%	$13.9231	$13.92	$13.90	$13.90
Purchase #2	$138.97	8.485%	$150.7616	$150.76	$150.75	$150.80
Purchase #3	$198.32	10.826%	$219.7901	$219.79	$219.80	$219.80
Purchase #4	$47.69	13.758%	$54.2512	$54.25	$54.25	$54.30
Purchase #5	$15.77	11.236%	$17.5419	$17.54	$17.55	$17.50
Purchase #6	$65.78	10.606%	$72.7566	$72.76	$72.75	$72.80
Purchase #7	$65.28	12.266%	$73.2872	$73.29	$73.30	$73.30
7 purchase totals =	$545.11		$602.3117	$602.31	$602.30	$602.40