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	$16.58	10.803%	$18.3711	$18.37	$18.35	$18.40
Purchase #2	$39.45	13.730%	$44.8665	$44.87	$44.85	$44.90
Purchase #3	$101.47	11.199%	$112.8336	$112.83	$112.85	$112.80
Purchase #4	$111.30	11.176%	$123.7389	$123.74	$123.75	$123.70
Purchase #5	$127.55	7.384%	$136.9683	$136.97	$136.95	$137.00
Purchase #6	$143.25	4.628%	$149.8796	$149.88	$149.90	$149.90
Purchase #7	$127.41	12.616%	$143.484	$143.48	$143.50	$143.50
7 purchase totals =	$667.01		$730.1420	$730.14	$730.15	$730.20