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	$38.99	11.809%	$43.5943	$43.59	$43.60	$43.60
Purchase #2	$105.31	6.171%	$111.8087	$111.81	$111.80	$111.80
Purchase #3	$189.28	11.445%	$210.9431	$210.94	$210.95	$210.90
Purchase #4	$146.70	13.550%	$166.5779	$166.58	$166.60	$166.60
Purchase #5	$207.65	8.325%	$224.9369	$224.94	$224.95	$224.90
Purchase #6	$150.97	6.139%	$160.238	$160.24	$160.25	$160.20
Purchase #7	$106.25	13.206%	$120.2814	$120.28	$120.30	$120.30
7 purchase totals =	$945.15		$1,038.3803	$1,038.38	$1,038.45	$1,038.30