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	$244.61	13.806%	$278.3809	$278.38	$278.40	$278.40
Purchase #2	$180.95	6.746%	$193.1569	$193.16	$193.15	$193.20
Purchase #3	$231.70	11.709%	$258.8298	$258.83	$258.85	$258.80
Purchase #4	$94.54	10.636%	$104.5953	$104.60	$104.60	$104.60
Purchase #5	$19.57	11.404%	$21.8018	$21.80	$21.80	$21.80
Purchase #6	$39.28	7.363%	$42.1722	$42.17	$42.15	$42.20
Purchase #7	$190.45	3.620%	$197.3443	$197.34	$197.35	$197.30
7 purchase totals =	$1,001.10		$1,096.2812	$1,096.28	$1,096.30	$1,096.30