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	$104.40	12.850%	$117.8154	$117.82	$117.80	$117.80
Purchase #2	$147.67	5.421%	$155.6752	$155.68	$155.70	$155.70
Purchase #3	$237.51	7.163%	$254.5228	$254.52	$254.50	$254.50
Purchase #4	$40.54	8.402%	$43.9462	$43.95	$43.95	$43.90
Purchase #5	$89.73	11.552%	$100.0956	$100.10	$100.10	$100.10
Purchase #6	$108.88	13.392%	$123.4612	$123.46	$123.45	$123.50
Purchase #7	$132.28	4.503%	$138.2366	$138.24	$138.25	$138.20
7 purchase totals =	$861.01		$933.7530	$933.77	$933.75	$933.70