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	$13.91	13.602%	$15.802	$15.80	$15.80	$15.80
Purchase #2	$132.92	12.779%	$149.9058	$149.91	$149.90	$149.90
Purchase #3	$50.88	7.295%	$54.5917	$54.59	$54.60	$54.60
Purchase #4	$20.84	3.418%	$21.5523	$21.55	$21.55	$21.60
Purchase #5	$80.53	8.654%	$87.4991	$87.50	$87.50	$87.50
Purchase #6	$45.55	6.654%	$48.5809	$48.58	$48.60	$48.60
Purchase #7	$174.92	12.216%	$196.2882	$196.29	$196.30	$196.30
7 purchase totals =	$519.55		$574.2200	$574.22	$574.25	$574.30