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	$250.77	3.492%	$259.5269	$259.53	$259.55	$259.50
Purchase #2	$98.25	10.540%	$108.6056	$108.61	$108.60	$108.60
Purchase #3	$126.60	8.857%	$137.813	$137.81	$137.80	$137.80
Purchase #4	$16.84	3.756%	$17.4725	$17.47	$17.45	$17.50
Purchase #5	$90.36	9.714%	$99.1376	$99.14	$99.15	$99.10
Purchase #6	$38.59	8.739%	$41.9624	$41.96	$41.95	$42.00
Purchase #7	$54.56	13.221%	$61.7734	$61.77	$61.75	$61.80
7 purchase totals =	$675.97		$726.2914	$726.29	$726.25	$726.30