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	$12.28	3.542%	$12.715	$12.72	$12.70	$12.70
Purchase #2	$14.50	13.609%	$16.4733	$16.47	$16.45	$16.50
Purchase #3	$76.56	5.607%	$80.8527	$80.85	$80.85	$80.90
Purchase #4	$71.86	6.751%	$76.7113	$76.71	$76.70	$76.70
Purchase #5	$137.54	4.166%	$143.2699	$143.27	$143.25	$143.30
Purchase #6	$68.91	3.644%	$71.4211	$71.42	$71.40	$71.40
Purchase #7	$80.41	12.171%	$90.1967	$90.20	$90.20	$90.20
7 purchase totals =	$462.06		$491.6400	$491.64	$491.55	$491.70