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	$234.53	6.315%	$249.3406	$249.34	$249.35	$249.30
Purchase #2	$70.95	12.583%	$79.8776	$79.88	$79.90	$79.90
Purchase #3	$157.90	9.786%	$173.3521	$173.35	$173.35	$173.40
Purchase #4	$59.47	13.496%	$67.4961	$67.50	$67.50	$67.50
Purchase #5	$132.72	6.520%	$141.3733	$141.37	$141.35	$141.40
Purchase #6	$37.73	9.520%	$41.3219	$41.32	$41.30	$41.30
Purchase #7	$178.65	5.848%	$189.0975	$189.10	$189.10	$189.10
7 purchase totals =	$871.95		$941.8591	$941.86	$941.85	$941.90