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	$123.31	5.845%	$130.5175	$130.52	$130.50	$130.50
Purchase #2	$214.74	11.523%	$239.4845	$239.48	$239.50	$239.50
Purchase #3	$79.68	13.428%	$90.3794	$90.38	$90.40	$90.40
Purchase #4	$84.37	6.357%	$89.7334	$89.73	$89.75	$89.70
Purchase #5	$173.50	7.626%	$186.7311	$186.73	$186.75	$186.70
Purchase #6	$92.66	5.575%	$97.8258	$97.83	$97.85	$97.80
Purchase #7	$93.27	13.375%	$105.7449	$105.74	$105.75	$105.70
7 purchase totals =	$861.53		$940.4166	$940.41	$940.50	$940.30