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	$15.94	10.335%	$17.5874	$17.59	$17.60	$17.60
Purchase #2	$120.33	10.795%	$133.3196	$133.32	$133.30	$133.30
Purchase #3	$172.87	3.141%	$178.2998	$178.30	$178.30	$178.30
Purchase #4	$119.58	10.152%	$131.7198	$131.72	$131.70	$131.70
Purchase #5	$24.34	11.157%	$27.0556	$27.06	$27.05	$27.10
Purchase #6	$225.79	13.119%	$255.4114	$255.41	$255.40	$255.40
Purchase #7	$29.75	3.787%	$30.8766	$30.88	$30.90	$30.90
7 purchase totals =	$708.60		$774.2702	$774.28	$774.25	$774.30