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	$19.64	4.798%	$20.5823	$20.58	$20.60	$20.60
Purchase #2	$102.92	6.235%	$109.3371	$109.34	$109.35	$109.30
Purchase #3	$60.98	8.670%	$66.267	$66.27	$66.25	$66.30
Purchase #4	$59.58	9.628%	$65.3164	$65.32	$65.30	$65.30
Purchase #5	$135.42	4.375%	$141.3446	$141.34	$141.35	$141.30
Purchase #6	$217.31	4.689%	$227.4997	$227.50	$227.50	$227.50
Purchase #7	$62.46	9.350%	$68.3	$68.30	$68.30	$68.30
7 purchase totals =	$658.31		$698.6471	$698.65	$698.65	$698.60