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	$53.60	11.379%	$59.6991	$59.70	$59.70	$59.70
Purchase #2	$62.39	5.754%	$65.9799	$65.98	$66.00	$66.00
Purchase #3	$57.40	8.524%	$62.2928	$62.29	$62.30	$62.30
Purchase #4	$59.91	10.664%	$66.2988	$66.30	$66.30	$66.30
Purchase #5	$130.26	8.351%	$141.138	$141.14	$141.15	$141.10
Purchase #6	$228.89	5.817%	$242.2045	$242.20	$242.20	$242.20
Purchase #7	$52.46	9.215%	$57.2942	$57.29	$57.30	$57.30
7 purchase totals =	$644.91		$694.9073	$694.90	$694.95	$694.90