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	$183.83	3.573%	$190.3982	$190.40	$190.40	$190.40
Purchase #2	$192.42	8.626%	$209.0181	$209.02	$209.00	$209.00
Purchase #3	$201.45	11.322%	$224.2582	$224.26	$224.25	$224.30
Purchase #4	$19.38	12.720%	$21.8451	$21.85	$21.85	$21.80
Purchase #5	$98.89	4.287%	$103.1294	$103.13	$103.15	$103.10
Purchase #6	$208.69	4.299%	$217.6616	$217.66	$217.65	$217.70
Purchase #7	$103.36	7.688%	$111.3063	$111.31	$111.30	$111.30
7 purchase totals =	$1,008.02		$1,077.6169	$1,077.63	$1,077.60	$1,077.60