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	$110.43	7.342%	$118.5378	$118.54	$118.55	$118.50
Purchase #2	$122.44	4.229%	$127.618	$127.62	$127.60	$127.60
Purchase #3	$152.52	8.636%	$165.6916	$165.69	$165.70	$165.70
Purchase #4	$231.44	6.193%	$245.7731	$245.77	$245.75	$245.80
Purchase #5	$6.72	9.749%	$7.3751	$7.38	$7.40	$7.40
Purchase #6	$80.28	12.500%	$90.315	$90.32	$90.30	$90.30
Purchase #7	$86.94	6.609%	$92.6859	$92.69	$92.70	$92.70
7 purchase totals =	$790.77		$847.9965	$848.01	$848.00	$848.00