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	$87.29	3.740%	$90.5546	$90.55	$90.55	$90.60
Purchase #2	$45.92	5.110%	$48.2665	$48.27	$48.25	$48.30
Purchase #3	$29.53	7.831%	$31.8425	$31.84	$31.85	$31.80
Purchase #4	$125.39	10.269%	$138.2663	$138.27	$138.25	$138.30
Purchase #5	$93.54	8.243%	$101.2505	$101.25	$101.25	$101.30
Purchase #6	$115.65	10.161%	$127.4012	$127.40	$127.40	$127.40
Purchase #7	$138.67	9.758%	$152.2014	$152.20	$152.20	$152.20
7 purchase totals =	$635.99		$689.7830	$689.78	$689.75	$689.90