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	$39.73	6.322%	$42.2417	$42.24	$42.25	$42.20
Purchase #2	$90.73	6.598%	$96.7164	$96.72	$96.70	$96.70
Purchase #3	$87.36	9.424%	$95.5928	$95.59	$95.60	$95.60
Purchase #4	$163.98	9.633%	$179.7762	$179.78	$179.80	$179.80
Purchase #5	$164.99	13.812%	$187.7784	$187.78	$187.80	$187.80
Purchase #6	$134.64	7.204%	$144.3395	$144.34	$144.35	$144.30
Purchase #7	$207.89	10.660%	$230.0511	$230.05	$230.05	$230.10
7 purchase totals =	$889.32		$976.4961	$976.50	$976.55	$976.50