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	$15.32	7.736%	$16.5052	$16.51	$16.50	$16.50
Purchase #2	$59.70	4.830%	$62.5835	$62.58	$62.60	$62.60
Purchase #3	$53.74	8.641%	$58.3837	$58.38	$58.40	$58.40
Purchase #4	$219.55	5.205%	$230.9776	$230.98	$231.00	$231.00
Purchase #5	$93.45	6.386%	$99.4177	$99.42	$99.40	$99.40
Purchase #6	$61.46	5.121%	$64.6074	$64.61	$64.60	$64.60
Purchase #7	$159.90	12.326%	$179.6093	$179.61	$179.60	$179.60
7 purchase totals =	$663.12		$712.0844	$712.09	$712.10	$712.10