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	$20.40	7.270%	$21.8831	$21.88	$21.90	$21.90
Purchase #2	$153.66	9.651%	$168.4897	$168.49	$168.50	$168.50
Purchase #3	$169.41	9.646%	$185.7513	$185.75	$185.75	$185.80
Purchase #4	$46.44	5.175%	$48.8433	$48.84	$48.85	$48.80
Purchase #5	$111.31	5.446%	$117.3719	$117.37	$117.35	$117.40
Purchase #6	$241.79	4.194%	$251.9307	$251.93	$251.95	$251.90
Purchase #7	$193.58	3.103%	$199.5868	$199.59	$199.60	$199.60
7 purchase totals =	$936.59		$993.8568	$993.85	$993.90	$993.90