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	$44.59	13.778%	$50.7336	$50.73	$50.75	$50.70
Purchase #2	$180.70	8.697%	$196.4155	$196.42	$196.40	$196.40
Purchase #3	$30.62	3.130%	$31.5784	$31.58	$31.60	$31.60
Purchase #4	$233.88	9.842%	$256.8985	$256.90	$256.90	$256.90
Purchase #5	$140.37	13.133%	$158.8048	$158.80	$158.80	$158.80
Purchase #6	$34.69	12.360%	$38.9777	$38.98	$39.00	$39.00
Purchase #7	$61.78	11.330%	$68.7797	$68.78	$68.80	$68.80
7 purchase totals =	$726.63		$802.1882	$802.19	$802.25	$802.20