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	$150.90	13.546%	$171.3409	$171.34	$171.35	$171.30
Purchase #2	$155.42	10.785%	$172.182	$172.18	$172.20	$172.20
Purchase #3	$61.63	4.599%	$64.4644	$64.46	$64.45	$64.50
Purchase #4	$180.90	10.537%	$199.9614	$199.96	$199.95	$200.00
Purchase #5	$97.39	7.231%	$104.4323	$104.43	$104.45	$104.40
Purchase #6	$241.80	8.548%	$262.4691	$262.47	$262.45	$262.50
Purchase #7	$22.84	6.734%	$24.378	$24.38	$24.40	$24.40
7 purchase totals =	$910.88		$999.2281	$999.22	$999.25	$999.30