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	$49.92	6.641%	$53.2352	$53.24	$53.25	$53.20
Purchase #2	$46.51	12.312%	$52.2363	$52.24	$52.25	$52.20
Purchase #3	$38.65	9.253%	$42.2263	$42.23	$42.25	$42.20
Purchase #4	$51.38	6.105%	$54.5167	$54.52	$54.50	$54.50
Purchase #5	$28.32	7.487%	$30.4403	$30.44	$30.45	$30.40
Purchase #6	$192.97	10.132%	$212.5217	$212.52	$212.50	$212.50
Purchase #7	$178.71	10.133%	$196.8187	$196.82	$196.80	$196.80
7 purchase totals =	$586.46		$641.9952	$642.01	$642.00	$641.80