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	$135.51	4.647%	$141.8071	$141.81	$141.80	$141.80
Purchase #2	$15.54	9.156%	$16.9628	$16.96	$16.95	$17.00
Purchase #3	$79.50	10.629%	$87.9501	$87.95	$87.95	$88.00
Purchase #4	$65.31	7.830%	$70.4238	$70.42	$70.40	$70.40
Purchase #5	$105.96	5.117%	$111.382	$111.38	$111.40	$111.40
Purchase #6	$139.79	3.290%	$144.3891	$144.39	$144.40	$144.40
Purchase #7	$99.85	5.723%	$105.5644	$105.56	$105.55	$105.60
7 purchase totals =	$641.46		$678.4793	$678.47	$678.45	$678.60