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	$153.50	12.841%	$173.2109	$173.21	$173.20	$173.20
Purchase #2	$24.91	8.353%	$26.9907	$26.99	$27.00	$27.00
Purchase #3	$81.60	9.350%	$89.2296	$89.23	$89.25	$89.20
Purchase #4	$152.93	6.240%	$162.4728	$162.47	$162.45	$162.50
Purchase #5	$156.38	13.162%	$176.9627	$176.96	$176.95	$177.00
Purchase #6	$97.30	8.338%	$105.4129	$105.41	$105.40	$105.40
Purchase #7	$53.78	3.478%	$55.6505	$55.65	$55.65	$55.70
7 purchase totals =	$720.40		$789.9301	$789.92	$789.90	$790.00