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	$149.31	6.794%	$159.4541	$159.45	$159.45	$159.50
Purchase #2	$40.59	4.857%	$42.5615	$42.56	$42.55	$42.60
Purchase #3	$95.61	7.500%	$102.7808	$102.78	$102.80	$102.80
Purchase #4	$89.54	11.624%	$99.9481	$99.95	$99.95	$99.90
Purchase #5	$89.66	11.286%	$99.779	$99.78	$99.80	$99.80
Purchase #6	$190.58	12.633%	$214.656	$214.66	$214.65	$214.70
Purchase #7	$129.48	5.844%	$137.0468	$137.05	$137.05	$137.00
7 purchase totals =	$784.77		$856.2263	$856.23	$856.25	$856.30