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	$70.42	9.551%	$77.1458	$77.15	$77.15	$77.10
Purchase #2	$170.36	8.153%	$184.2495	$184.25	$184.25	$184.20
Purchase #3	$45.50	12.369%	$51.1279	$51.13	$51.15	$51.10
Purchase #4	$131.31	6.331%	$139.6232	$139.62	$139.60	$139.60
Purchase #5	$64.82	7.728%	$69.8293	$69.83	$69.85	$69.80
Purchase #6	$166.76	10.828%	$184.8168	$184.82	$184.80	$184.80
Purchase #7	$177.87	12.380%	$199.8903	$199.89	$199.90	$199.90
7 purchase totals =	$827.04		$906.6828	$906.69	$906.70	$906.50