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	$150.30	9.446%	$164.4973	$164.50	$164.50	$164.50
Purchase #2	$53.63	4.439%	$56.0106	$56.01	$56.00	$56.00
Purchase #3	$48.96	10.558%	$54.1292	$54.13	$54.15	$54.10
Purchase #4	$200.73	13.377%	$227.5817	$227.58	$227.60	$227.60
Purchase #5	$99.52	5.778%	$105.2703	$105.27	$105.25	$105.30
Purchase #6	$179.67	9.848%	$197.3639	$197.36	$197.35	$197.40
Purchase #7	$18.55	10.729%	$20.5402	$20.54	$20.55	$20.50
7 purchase totals =	$751.36		$825.3932	$825.39	$825.40	$825.40