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	$35.32	8.567%	$38.3459	$38.35	$38.35	$38.30
Purchase #2	$204.30	13.572%	$232.0276	$232.03	$232.05	$232.00
Purchase #3	$147.88	11.431%	$164.7842	$164.78	$164.80	$164.80
Purchase #4	$103.60	8.366%	$112.2672	$112.27	$112.25	$112.30
Purchase #5	$109.89	8.379%	$119.0977	$119.10	$119.10	$119.10
Purchase #6	$50.25	6.491%	$53.5117	$53.51	$53.50	$53.50
Purchase #7	$55.94	12.307%	$62.8245	$62.82	$62.80	$62.80
7 purchase totals =	$707.18		$782.8588	$782.86	$782.85	$782.80