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	$106.47	5.670%	$112.5068	$112.51	$112.50	$112.50
Purchase #2	$76.29	13.816%	$86.8302	$86.83	$86.85	$86.80
Purchase #3	$152.57	10.716%	$168.9194	$168.92	$168.90	$168.90
Purchase #4	$126.96	5.736%	$134.2424	$134.24	$134.25	$134.20
Purchase #5	$173.37	12.247%	$194.6026	$194.60	$194.60	$194.60
Purchase #6	$223.27	6.513%	$237.8116	$237.81	$237.80	$237.80
Purchase #7	$190.77	7.215%	$204.5341	$204.53	$204.55	$204.50
7 purchase totals =	$1,049.70		$1,139.4471	$1,139.44	$1,139.45	$1,139.30