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	$50.61	13.367%	$57.375	$57.38	$57.40	$57.40
Purchase #2	$96.51	7.425%	$103.6759	$103.68	$103.70	$103.70
Purchase #3	$152.32	4.339%	$158.9292	$158.93	$158.95	$158.90
Purchase #4	$12.72	7.500%	$13.674	$13.67	$13.65	$13.70
Purchase #5	$80.75	3.188%	$83.3243	$83.32	$83.30	$83.30
Purchase #6	$137.39	9.361%	$150.2511	$150.25	$150.25	$150.30
Purchase #7	$111.30	10.729%	$123.2414	$123.24	$123.25	$123.20
7 purchase totals =	$641.60		$690.4709	$690.47	$690.50	$690.50