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	$43.69	7.267%	$46.865	$46.87	$46.85	$46.90
Purchase #2	$168.89	12.638%	$190.2343	$190.23	$190.25	$190.20
Purchase #3	$116.72	10.165%	$128.5846	$128.58	$128.60	$128.60
Purchase #4	$39.94	9.717%	$43.821	$43.82	$43.80	$43.80
Purchase #5	$65.87	7.368%	$70.7233	$70.72	$70.70	$70.70
Purchase #6	$240.71	4.408%	$251.3205	$251.32	$251.30	$251.30
Purchase #7	$42.78	3.506%	$44.2799	$44.28	$44.30	$44.30
7 purchase totals =	$718.60		$775.8286	$775.82	$775.80	$775.80