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	$16.73	6.304%	$17.7847	$17.78	$17.80	$17.80
Purchase #2	$47.85	11.708%	$53.4523	$53.45	$53.45	$53.50
Purchase #3	$31.60	6.139%	$33.5399	$33.54	$33.55	$33.50
Purchase #4	$19.31	8.606%	$20.9718	$20.97	$20.95	$21.00
Purchase #5	$171.73	4.154%	$178.8637	$178.86	$178.85	$178.90
Purchase #6	$161.41	11.257%	$179.5799	$179.58	$179.60	$179.60
Purchase #7	$81.49	5.439%	$85.9222	$85.92	$85.90	$85.90
7 purchase totals =	$530.12		$570.1145	$570.10	$570.10	$570.20