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	$208.45	9.436%	$228.1193	$228.12	$228.10	$228.10
Purchase #2	$56.27	13.649%	$63.9503	$63.95	$63.95	$64.00
Purchase #3	$57.86	8.580%	$62.8244	$62.82	$62.80	$62.80
Purchase #4	$134.39	13.320%	$152.2907	$152.29	$152.30	$152.30
Purchase #5	$23.33	9.782%	$25.6121	$25.61	$25.60	$25.60
Purchase #6	$90.50	10.576%	$100.0713	$100.07	$100.05	$100.10
Purchase #7	$29.89	13.501%	$33.9254	$33.93	$33.95	$33.90
7 purchase totals =	$600.69		$666.7935	$666.79	$666.75	$666.80