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	$67.72	8.241%	$73.3008	$73.30	$73.30	$73.30
Purchase #2	$118.96	9.799%	$130.6169	$130.62	$130.60	$130.60
Purchase #3	$96.85	6.176%	$102.8315	$102.83	$102.85	$102.80
Purchase #4	$162.57	6.159%	$172.5827	$172.58	$172.60	$172.60
Purchase #5	$106.51	5.171%	$112.0176	$112.02	$112.00	$112.00
Purchase #6	$118.89	10.576%	$131.4638	$131.46	$131.45	$131.50
Purchase #7	$144.90	12.247%	$162.6459	$162.65	$162.65	$162.60
7 purchase totals =	$816.40		$885.4592	$885.46	$885.45	$885.40