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	$10.88	11.850%	$12.1693	$12.17	$12.15	$12.20
Purchase #2	$77.50	4.130%	$80.7008	$80.70	$80.70	$80.70
Purchase #3	$105.56	10.544%	$116.6902	$116.69	$116.70	$116.70
Purchase #4	$169.48	9.146%	$184.9806	$184.98	$185.00	$185.00
Purchase #5	$110.85	5.164%	$116.5743	$116.57	$116.55	$116.60
Purchase #6	$57.80	6.569%	$61.5969	$61.60	$61.60	$61.60
Purchase #7	$32.41	9.777%	$35.5787	$35.58	$35.60	$35.60
7 purchase totals =	$564.48		$608.2908	$608.29	$608.30	$608.40