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	$128.58	5.823%	$136.0672	$136.07	$136.05	$136.10
Purchase #2	$151.46	13.312%	$171.6224	$171.62	$171.60	$171.60
Purchase #3	$98.84	4.541%	$103.3283	$103.33	$103.35	$103.30
Purchase #4	$96.59	12.337%	$108.5063	$108.51	$108.50	$108.50
Purchase #5	$21.64	13.806%	$24.6276	$24.63	$24.65	$24.60
Purchase #6	$64.91	3.528%	$67.2	$67.20	$67.20	$67.20
Purchase #7	$9.62	9.670%	$10.5503	$10.55	$10.55	$10.60
7 purchase totals =	$571.64		$621.9021	$621.91	$621.90	$621.90