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	$199.70	10.696%	$221.0599	$221.06	$221.05	$221.10
Purchase #2	$85.63	10.823%	$94.8977	$94.90	$94.90	$94.90
Purchase #3	$37.28	10.309%	$41.1232	$41.12	$41.10	$41.10
Purchase #4	$105.78	5.400%	$111.4921	$111.49	$111.50	$111.50
Purchase #5	$46.73	8.636%	$50.7656	$50.77	$50.75	$50.80
Purchase #6	$98.49	12.485%	$110.7865	$110.79	$110.80	$110.80
Purchase #7	$200.42	10.395%	$221.2537	$221.25	$221.25	$221.30
7 purchase totals =	$774.03		$851.3787	$851.38	$851.35	$851.50