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	$218.47	10.233%	$240.826	$240.83	$240.85	$240.80
Purchase #2	$124.26	4.630%	$130.0132	$130.01	$130.00	$130.00
Purchase #3	$32.81	3.411%	$33.9291	$33.93	$33.95	$33.90
Purchase #4	$34.85	7.116%	$37.3299	$37.33	$37.35	$37.30
Purchase #5	$42.94	6.146%	$45.5791	$45.58	$45.60	$45.60
Purchase #6	$240.29	5.351%	$253.1479	$253.15	$253.15	$253.10
Purchase #7	$179.42	10.870%	$198.923	$198.92	$198.90	$198.90
7 purchase totals =	$873.04		$939.7482	$939.75	$939.80	$939.60