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	$99.54	6.408%	$105.9185	$105.92	$105.90	$105.90
Purchase #2	$221.40	11.487%	$246.8322	$246.83	$246.85	$246.80
Purchase #3	$27.74	7.578%	$29.8421	$29.84	$29.85	$29.80
Purchase #4	$56.38	7.244%	$60.4642	$60.46	$60.45	$60.50
Purchase #5	$186.68	11.630%	$208.3909	$208.39	$208.40	$208.40
Purchase #6	$127.40	9.735%	$139.8024	$139.80	$139.80	$139.80
Purchase #7	$35.49	5.236%	$37.3483	$37.35	$37.35	$37.30
7 purchase totals =	$754.63		$828.5986	$828.59	$828.60	$828.50