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	$15.95	13.735%	$18.1407	$18.14	$18.15	$18.10
Purchase #2	$104.81	4.161%	$109.1711	$109.17	$109.15	$109.20
Purchase #3	$244.42	11.122%	$271.6044	$271.60	$271.60	$271.60
Purchase #4	$30.26	3.707%	$31.3817	$31.38	$31.40	$31.40
Purchase #5	$29.85	9.147%	$32.5804	$32.58	$32.60	$32.60
Purchase #6	$28.82	11.793%	$32.2187	$32.22	$32.20	$32.20
Purchase #7	$244.63	5.828%	$258.887	$258.89	$258.90	$258.90
7 purchase totals =	$698.74		$753.9840	$753.98	$754.00	$754.00