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	$35.30	5.693%	$37.3096	$37.31	$37.30	$37.30
Purchase #2	$167.86	10.143%	$184.886	$184.89	$184.90	$184.90
Purchase #3	$64.89	11.661%	$72.4568	$72.46	$72.45	$72.50
Purchase #4	$39.25	5.733%	$41.5002	$41.50	$41.50	$41.50
Purchase #5	$122.39	6.540%	$130.3943	$130.39	$130.40	$130.40
Purchase #6	$192.93	11.300%	$214.7311	$214.73	$214.75	$214.70
Purchase #7	$182.62	7.723%	$196.7237	$196.72	$196.70	$196.70
7 purchase totals =	$805.24		$878.0017	$878.00	$878.00	$878.00