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	$84.57	5.290%	$89.0438	$89.04	$89.05	$89.00
Purchase #2	$83.81	7.499%	$90.0949	$90.09	$90.10	$90.10
Purchase #3	$29.80	8.465%	$32.3226	$32.32	$32.30	$32.30
Purchase #4	$158.39	5.291%	$166.7704	$166.77	$166.75	$166.80
Purchase #5	$66.61	9.405%	$72.8747	$72.87	$72.85	$72.90
Purchase #6	$61.39	5.591%	$64.8223	$64.82	$64.80	$64.80
Purchase #7	$153.33	8.580%	$166.4857	$166.49	$166.50	$166.50
7 purchase totals =	$637.90		$682.4144	$682.40	$682.35	$682.40