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	$57.36	8.823%	$62.4209	$62.42	$62.40	$62.40
Purchase #2	$171.35	12.811%	$193.3016	$193.30	$193.30	$193.30
Purchase #3	$120.30	6.231%	$127.7959	$127.80	$127.80	$127.80
Purchase #4	$11.59	8.644%	$12.5918	$12.59	$12.60	$12.60
Purchase #5	$171.27	10.495%	$189.2448	$189.24	$189.25	$189.20
Purchase #6	$76.69	7.437%	$82.3934	$82.39	$82.40	$82.40
Purchase #7	$134.38	4.321%	$140.1866	$140.19	$140.20	$140.20
7 purchase totals =	$742.94		$807.9350	$807.93	$807.95	$807.90