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	$17.74	6.555%	$18.9029	$18.90	$18.90	$18.90
Purchase #2	$237.57	12.259%	$266.6937	$266.69	$266.70	$266.70
Purchase #3	$208.46	8.183%	$225.5183	$225.52	$225.50	$225.50
Purchase #4	$245.86	8.136%	$265.8632	$265.86	$265.85	$265.90
Purchase #5	$54.77	5.666%	$57.8733	$57.87	$57.85	$57.90
Purchase #6	$108.30	8.118%	$117.0918	$117.09	$117.10	$117.10
Purchase #7	$57.55	13.842%	$65.5161	$65.52	$65.50	$65.50
7 purchase totals =	$930.25		$1,017.4593	$1,017.45	$1,017.40	$1,017.50