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	$48.29	9.784%	$53.0147	$53.01	$53.00	$53.00
Purchase #2	$137.78	3.171%	$142.149	$142.15	$142.15	$142.10
Purchase #3	$61.91	8.418%	$67.1216	$67.12	$67.10	$67.10
Purchase #4	$172.42	5.346%	$181.6376	$181.64	$181.65	$181.60
Purchase #5	$140.81	3.504%	$145.744	$145.74	$145.75	$145.70
Purchase #6	$160.54	6.660%	$171.232	$171.23	$171.25	$171.20
Purchase #7	$57.38	6.480%	$61.0982	$61.10	$61.10	$61.10
7 purchase totals =	$779.13		$821.9971	$821.99	$822.00	$821.80