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	$131.91	10.245%	$145.4242	$145.42	$145.40	$145.40
Purchase #2	$39.93	12.141%	$44.7779	$44.78	$44.80	$44.80
Purchase #3	$76.81	12.837%	$86.6701	$86.67	$86.65	$86.70
Purchase #4	$40.29	7.352%	$43.2521	$43.25	$43.25	$43.30
Purchase #5	$164.80	4.787%	$172.689	$172.69	$172.70	$172.70
Purchase #6	$33.96	11.510%	$37.8688	$37.87	$37.85	$37.90
Purchase #7	$149.32	6.662%	$159.2677	$159.27	$159.25	$159.30
7 purchase totals =	$637.02		$689.9498	$689.95	$689.90	$690.10