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	$137.51	7.810%	$148.2495	$148.25	$148.25	$148.20
Purchase #2	$63.47	13.689%	$72.1584	$72.16	$72.15	$72.20
Purchase #3	$94.62	11.460%	$105.4635	$105.46	$105.45	$105.50
Purchase #4	$66.69	11.635%	$74.4494	$74.45	$74.45	$74.40
Purchase #5	$89.63	4.701%	$93.8435	$93.84	$93.85	$93.80
Purchase #6	$206.52	13.547%	$234.4973	$234.50	$234.50	$234.50
Purchase #7	$183.47	4.196%	$191.1684	$191.17	$191.15	$191.20
7 purchase totals =	$841.91		$919.8300	$919.83	$919.80	$919.80