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	$46.26	6.664%	$49.3428	$49.34	$49.35	$49.30
Purchase #2	$109.89	6.149%	$116.6471	$116.65	$116.65	$116.60
Purchase #3	$240.35	12.129%	$269.5021	$269.50	$269.50	$269.50
Purchase #4	$223.38	6.624%	$238.1767	$238.18	$238.20	$238.20
Purchase #5	$131.45	11.114%	$146.0594	$146.06	$146.05	$146.10
Purchase #6	$212.59	13.782%	$241.8892	$241.89	$241.90	$241.90
Purchase #7	$24.70	12.213%	$27.7166	$27.72	$27.70	$27.70
7 purchase totals =	$988.62		$1,089.3339	$1,089.34	$1,089.35	$1,089.30