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	$89.80	12.139%	$100.7008	$100.70	$100.70	$100.70
Purchase #2	$228.69	13.526%	$259.6226	$259.62	$259.60	$259.60
Purchase #3	$147.44	10.462%	$162.8652	$162.87	$162.85	$162.90
Purchase #4	$225.93	3.248%	$233.2682	$233.27	$233.25	$233.30
Purchase #5	$229.96	10.561%	$254.2461	$254.25	$254.25	$254.20
Purchase #6	$228.27	9.335%	$249.579	$249.58	$249.60	$249.60
Purchase #7	$135.98	10.785%	$150.6454	$150.65	$150.65	$150.60
7 purchase totals =	$1,286.07		$1,410.9273	$1,410.94	$1,410.90	$1,410.90