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	$131.71	4.134%	$137.1549	$137.15	$137.15	$137.20
Purchase #2	$105.97	13.104%	$119.8563	$119.86	$119.85	$119.90
Purchase #3	$174.91	3.772%	$181.5076	$181.51	$181.50	$181.50
Purchase #4	$42.34	13.531%	$48.069	$48.07	$48.05	$48.10
Purchase #5	$14.45	6.361%	$15.3692	$15.37	$15.35	$15.40
Purchase #6	$41.52	7.861%	$44.7839	$44.78	$44.80	$44.80
Purchase #7	$104.86	8.331%	$113.5959	$113.60	$113.60	$113.60
7 purchase totals =	$615.76		$660.3368	$660.34	$660.30	$660.50