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	$94.86	6.162%	$100.7053	$100.71	$100.70	$100.70
Purchase #2	$129.73	5.323%	$136.6355	$136.64	$136.65	$136.60
Purchase #3	$202.31	6.167%	$214.7865	$214.79	$214.80	$214.80
Purchase #4	$69.31	3.805%	$71.9472	$71.95	$71.95	$71.90
Purchase #5	$45.56	7.146%	$48.8157	$48.82	$48.80	$48.80
Purchase #6	$92.28	12.485%	$103.8012	$103.80	$103.80	$103.80
Purchase #7	$40.33	8.749%	$43.8585	$43.86	$43.85	$43.90
7 purchase totals =	$674.38		$720.5499	$720.57	$720.55	$720.50