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	$28.76	9.373%	$31.4557	$31.46	$31.45	$31.50
Purchase #2	$47.55	6.150%	$50.4743	$50.47	$50.45	$50.50
Purchase #3	$8.30	7.137%	$8.8924	$8.89	$8.90	$8.90
Purchase #4	$118.74	13.251%	$134.4742	$134.47	$134.45	$134.50
Purchase #5	$145.79	8.710%	$158.4883	$158.49	$158.50	$158.50
Purchase #6	$153.38	4.238%	$159.8802	$159.88	$159.90	$159.90
Purchase #7	$124.29	10.146%	$136.9005	$136.90	$136.90	$136.90
7 purchase totals =	$626.81		$680.5656	$680.56	$680.55	$680.70