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	$27.39	7.821%	$29.5322	$29.53	$29.55	$29.50
Purchase #2	$75.82	6.130%	$80.4678	$80.47	$80.45	$80.50
Purchase #3	$132.25	10.260%	$145.8189	$145.82	$145.80	$145.80
Purchase #4	$243.72	7.116%	$261.0631	$261.06	$261.05	$261.10
Purchase #5	$83.74	8.319%	$90.7063	$90.71	$90.70	$90.70
Purchase #6	$10.59	12.422%	$11.9055	$11.91	$11.90	$11.90
Purchase #7	$93.30	8.823%	$101.5319	$101.53	$101.55	$101.50
7 purchase totals =	$666.81		$721.0257	$721.03	$721.00	$721.00