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	$100.82	8.606%	$109.4966	$109.50	$109.50	$109.50
Purchase #2	$242.26	9.734%	$265.8416	$265.84	$265.85	$265.80
Purchase #3	$164.72	6.105%	$174.7762	$174.78	$174.80	$174.80
Purchase #4	$42.57	6.218%	$45.217	$45.22	$45.20	$45.20
Purchase #5	$211.41	5.215%	$222.435	$222.44	$222.45	$222.40
Purchase #6	$45.37	5.639%	$47.9284	$47.93	$47.95	$47.90
Purchase #7	$52.62	3.718%	$54.5764	$54.58	$54.60	$54.60
7 purchase totals =	$859.77		$920.2712	$920.29	$920.35	$920.20