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	$146.78	13.653%	$166.8199	$166.82	$166.80	$166.80
Purchase #2	$250.94	11.522%	$279.8533	$279.85	$279.85	$279.90
Purchase #3	$114.90	9.530%	$125.85	$125.85	$125.85	$125.90
Purchase #4	$126.50	4.635%	$132.3633	$132.36	$132.35	$132.40
Purchase #5	$202.73	9.714%	$222.4232	$222.42	$222.40	$222.40
Purchase #6	$61.26	7.581%	$65.9041	$65.90	$65.90	$65.90
Purchase #7	$115.79	7.867%	$124.8992	$124.90	$124.90	$124.90
7 purchase totals =	$1,018.90		$1,118.1130	$1,118.10	$1,118.05	$1,118.20