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	$54.52	12.393%	$61.2767	$61.28	$61.30	$61.30
Purchase #2	$167.89	11.511%	$187.2158	$187.22	$187.20	$187.20
Purchase #3	$223.93	9.643%	$245.5236	$245.52	$245.50	$245.50
Purchase #4	$103.47	10.839%	$114.6851	$114.69	$114.70	$114.70
Purchase #5	$31.79	10.103%	$35.0017	$35.00	$35.00	$35.00
Purchase #6	$52.50	4.458%	$54.8405	$54.84	$54.85	$54.80
Purchase #7	$130.47	8.464%	$141.513	$141.51	$141.50	$141.50
7 purchase totals =	$764.57		$840.0564	$840.06	$840.05	$840.00