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	$38.43	10.604%	$42.5051	$42.51	$42.50	$42.50
Purchase #2	$246.96	13.209%	$279.5809	$279.58	$279.60	$279.60
Purchase #3	$159.66	11.801%	$178.5015	$178.50	$178.50	$178.50
Purchase #4	$50.79	3.269%	$52.4503	$52.45	$52.45	$52.50
Purchase #5	$17.52	8.546%	$19.0173	$19.02	$19.00	$19.00
Purchase #6	$48.83	7.224%	$52.3575	$52.36	$52.35	$52.40
Purchase #7	$67.88	8.146%	$73.4095	$73.41	$73.40	$73.40
7 purchase totals =	$630.07		$697.8221	$697.83	$697.80	$697.90