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	$41.77	9.864%	$45.8902	$45.89	$45.90	$45.90
Purchase #2	$133.43	12.714%	$150.3943	$150.39	$150.40	$150.40
Purchase #3	$61.35	10.153%	$67.5789	$67.58	$67.60	$67.60
Purchase #4	$212.99	6.602%	$227.0516	$227.05	$227.05	$227.10
Purchase #5	$61.81	5.528%	$65.2269	$65.23	$65.25	$65.20
Purchase #6	$171.52	4.167%	$178.6672	$178.67	$178.65	$178.70
Purchase #7	$67.74	9.737%	$74.3358	$74.34	$74.35	$74.30
7 purchase totals =	$750.61		$809.1449	$809.15	$809.20	$809.20