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	$63.79	4.804%	$66.8545	$66.85	$66.85	$66.90
Purchase #2	$51.57	13.464%	$58.5134	$58.51	$58.50	$58.50
Purchase #3	$60.89	3.493%	$63.0169	$63.02	$63.00	$63.00
Purchase #4	$131.52	4.185%	$137.0241	$137.02	$137.00	$137.00
Purchase #5	$181.72	12.284%	$204.0425	$204.04	$204.05	$204.00
Purchase #6	$112.86	12.838%	$127.349	$127.35	$127.35	$127.30
Purchase #7	$170.57	5.454%	$179.8729	$179.87	$179.85	$179.90
7 purchase totals =	$772.92		$836.6733	$836.66	$836.60	$836.60