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	$6.55	4.816%	$6.8654	$6.87	$6.85	$6.90
Purchase #2	$22.90	11.144%	$25.452	$25.45	$25.45	$25.50
Purchase #3	$30.57	11.385%	$34.0504	$34.05	$34.05	$34.10
Purchase #4	$153.54	7.595%	$165.2014	$165.20	$165.20	$165.20
Purchase #5	$224.37	11.120%	$249.3199	$249.32	$249.30	$249.30
Purchase #6	$85.43	6.394%	$90.8924	$90.89	$90.90	$90.90
Purchase #7	$84.72	9.308%	$92.6057	$92.61	$92.60	$92.60
7 purchase totals =	$608.08		$664.3872	$664.39	$664.35	$664.50