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	$120.25	6.103%	$127.5889	$127.59	$127.60	$127.60
Purchase #2	$222.77	9.578%	$244.1069	$244.11	$244.10	$244.10
Purchase #3	$51.68	13.498%	$58.6558	$58.66	$58.65	$58.70
Purchase #4	$214.62	3.619%	$222.3871	$222.39	$222.40	$222.40
Purchase #5	$129.32	4.411%	$135.0243	$135.02	$135.00	$135.00
Purchase #6	$84.85	5.635%	$89.6313	$89.63	$89.65	$89.60
Purchase #7	$202.83	9.673%	$222.4497	$222.45	$222.45	$222.40
7 purchase totals =	$1,026.32		$1,099.8440	$1,099.85	$1,099.85	$1,099.80