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	$24.92	10.389%	$27.5089	$27.51	$27.50	$27.50
Purchase #2	$183.45	3.593%	$190.0414	$190.04	$190.05	$190.00
Purchase #3	$156.44	12.389%	$175.8214	$175.82	$175.80	$175.80
Purchase #4	$140.88	12.364%	$158.2984	$158.30	$158.30	$158.30
Purchase #5	$54.65	4.723%	$57.2311	$57.23	$57.25	$57.20
Purchase #6	$76.69	13.266%	$86.8637	$86.86	$86.85	$86.90
Purchase #7	$227.93	12.400%	$256.1933	$256.19	$256.20	$256.20
7 purchase totals =	$864.96		$951.9582	$951.95	$951.95	$951.90