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	$46.60	7.638%	$50.1593	$50.16	$50.15	$50.20
Purchase #2	$94.62	13.773%	$107.652	$107.65	$107.65	$107.70
Purchase #3	$56.73	4.110%	$59.0616	$59.06	$59.05	$59.10
Purchase #4	$129.98	7.229%	$139.3763	$139.38	$139.40	$139.40
Purchase #5	$13.93	12.422%	$15.6604	$15.66	$15.65	$15.70
Purchase #6	$169.79	12.408%	$190.8575	$190.86	$190.85	$190.90
Purchase #7	$7.36	7.414%	$7.9057	$7.91	$7.90	$7.90
7 purchase totals =	$519.01		$570.6728	$570.68	$570.65	$570.90