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	$82.47	9.741%	$90.5034	$90.50	$90.50	$90.50
Purchase #2	$140.98	13.548%	$160.08	$160.08	$160.10	$160.10
Purchase #3	$229.55	11.131%	$255.1012	$255.10	$255.10	$255.10
Purchase #4	$53.93	13.830%	$61.3885	$61.39	$61.40	$61.40
Purchase #5	$18.67	6.760%	$19.9321	$19.93	$19.95	$19.90
Purchase #6	$73.78	7.619%	$79.4013	$79.40	$79.40	$79.40
Purchase #7	$44.92	5.326%	$47.3124	$47.31	$47.30	$47.30
7 purchase totals =	$644.30		$713.7189	$713.71	$713.75	$713.70