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	$15.82	3.120%	$16.3136	$16.31	$16.30	$16.30
Purchase #2	$208.85	11.712%	$233.3105	$233.31	$233.30	$233.30
Purchase #3	$59.60	12.117%	$66.8217	$66.82	$66.80	$66.80
Purchase #4	$89.82	10.422%	$99.181	$99.18	$99.20	$99.20
Purchase #5	$24.38	4.799%	$25.55	$25.55	$25.55	$25.60
Purchase #6	$140.71	6.309%	$149.5874	$149.59	$149.60	$149.60
Purchase #7	$249.86	11.146%	$277.7094	$277.71	$277.70	$277.70
7 purchase totals =	$789.04		$868.4736	$868.47	$868.45	$868.50