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	$61.78	13.335%	$70.0184	$70.02	$70.00	$70.00
Purchase #2	$229.55	8.257%	$248.5039	$248.50	$248.50	$248.50
Purchase #3	$46.73	6.166%	$49.6114	$49.61	$49.60	$49.60
Purchase #4	$171.59	7.445%	$184.3649	$184.36	$184.35	$184.40
Purchase #5	$154.83	4.727%	$162.1488	$162.15	$162.15	$162.10
Purchase #6	$39.56	6.517%	$42.1381	$42.14	$42.15	$42.10
Purchase #7	$205.58	8.120%	$222.2731	$222.27	$222.25	$222.30
7 purchase totals =	$909.62		$979.0586	$979.05	$979.00	$979.00