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	$16.86	3.752%	$17.4926	$17.49	$17.50	$17.50
Purchase #2	$246.62	13.825%	$280.7152	$280.72	$280.70	$280.70
Purchase #3	$55.29	11.152%	$61.4559	$61.46	$61.45	$61.50
Purchase #4	$196.53	11.109%	$218.3625	$218.36	$218.35	$218.40
Purchase #5	$207.77	8.690%	$225.8252	$225.83	$225.85	$225.80
Purchase #6	$7.72	10.353%	$8.5193	$8.52	$8.50	$8.50
Purchase #7	$6.60	10.850%	$7.3161	$7.32	$7.30	$7.30
7 purchase totals =	$737.39		$819.6868	$819.70	$819.65	$819.70