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	$9.30	13.541%	$10.5593	$10.56	$10.55	$10.60
Purchase #2	$151.42	11.394%	$168.6728	$168.67	$168.65	$168.70
Purchase #3	$37.87	3.229%	$39.0928	$39.09	$39.10	$39.10
Purchase #4	$55.32	11.351%	$61.5994	$61.60	$61.60	$61.60
Purchase #5	$23.37	13.192%	$26.453	$26.45	$26.45	$26.50
Purchase #6	$169.46	10.671%	$187.5431	$187.54	$187.55	$187.50
Purchase #7	$28.71	11.625%	$32.0475	$32.05	$32.05	$32.00
7 purchase totals =	$475.45		$525.9679	$525.96	$525.95	$526.00