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	$61.91	7.193%	$66.3632	$66.36	$66.35	$66.40
Purchase #2	$31.67	13.234%	$35.8612	$35.86	$35.85	$35.90
Purchase #3	$242.55	8.204%	$262.4488	$262.45	$262.45	$262.40
Purchase #4	$137.39	9.747%	$150.7814	$150.78	$150.80	$150.80
Purchase #5	$200.62	8.215%	$217.1009	$217.10	$217.10	$217.10
Purchase #6	$138.59	5.321%	$145.9644	$145.96	$145.95	$146.00
Purchase #7	$94.44	6.221%	$100.3151	$100.32	$100.30	$100.30
7 purchase totals =	$907.17		$978.8350	$978.83	$978.80	$978.90