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	$49.40	12.286%	$55.4693	$55.47	$55.45	$55.50
Purchase #2	$185.59	4.810%	$194.5169	$194.52	$194.50	$194.50
Purchase #3	$245.43	5.681%	$259.3729	$259.37	$259.35	$259.40
Purchase #4	$92.70	13.376%	$105.0996	$105.10	$105.10	$105.10
Purchase #5	$99.55	5.820%	$105.3438	$105.34	$105.35	$105.30
Purchase #6	$206.53	9.123%	$225.3717	$225.37	$225.35	$225.40
Purchase #7	$204.47	8.235%	$221.3081	$221.31	$221.30	$221.30
7 purchase totals =	$1,083.67		$1,166.4823	$1,166.48	$1,166.40	$1,166.50