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	$245.78	11.107%	$273.0788	$273.08	$273.10	$273.10
Purchase #2	$152.54	11.417%	$169.9555	$169.96	$169.95	$170.00
Purchase #3	$7.45	10.169%	$8.2076	$8.21	$8.20	$8.20
Purchase #4	$50.50	8.493%	$54.789	$54.79	$54.80	$54.80
Purchase #5	$235.71	7.411%	$253.1785	$253.18	$253.20	$253.20
Purchase #6	$19.81	3.141%	$20.4322	$20.43	$20.45	$20.40
Purchase #7	$179.93	10.672%	$199.1321	$199.13	$199.15	$199.10
7 purchase totals =	$891.72		$978.7737	$978.78	$978.85	$978.80