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	$105.30	3.743%	$109.2414	$109.24	$109.25	$109.20
Purchase #2	$145.38	7.397%	$156.1338	$156.13	$156.15	$156.10
Purchase #3	$146.25	5.695%	$154.5789	$154.58	$154.60	$154.60
Purchase #4	$122.97	13.769%	$139.9017	$139.90	$139.90	$139.90
Purchase #5	$40.40	6.380%	$42.9775	$42.98	$43.00	$43.00
Purchase #6	$91.67	6.270%	$97.4177	$97.42	$97.40	$97.40
Purchase #7	$174.68	10.210%	$192.5148	$192.51	$192.50	$192.50
7 purchase totals =	$826.65		$892.7658	$892.76	$892.80	$892.70