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	$218.82	9.157%	$238.8573	$238.86	$238.85	$238.90
Purchase #2	$166.75	11.838%	$186.4899	$186.49	$186.50	$186.50
Purchase #3	$230.72	12.591%	$259.77	$259.77	$259.75	$259.80
Purchase #4	$85.39	3.342%	$88.2437	$88.24	$88.25	$88.20
Purchase #5	$106.49	11.697%	$118.9461	$118.95	$118.95	$118.90
Purchase #6	$193.90	10.768%	$214.7792	$214.78	$214.80	$214.80
Purchase #7	$140.44	5.550%	$148.2344	$148.23	$148.25	$148.20
7 purchase totals =	$1,142.51		$1,255.3206	$1,255.32	$1,255.35	$1,255.30