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	$19.76	9.524%	$21.6419	$21.64	$21.65	$21.60
Purchase #2	$140.34	9.599%	$153.8112	$153.81	$153.80	$153.80
Purchase #3	$54.60	5.278%	$57.4818	$57.48	$57.50	$57.50
Purchase #4	$70.99	10.778%	$78.6413	$78.64	$78.65	$78.60
Purchase #5	$29.92	12.369%	$33.6208	$33.62	$33.60	$33.60
Purchase #6	$152.37	5.121%	$160.1729	$160.17	$160.15	$160.20
Purchase #7	$63.93	10.224%	$70.4662	$70.47	$70.45	$70.50
7 purchase totals =	$531.91		$575.8361	$575.83	$575.80	$575.80