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	$204.89	6.801%	$218.8246	$218.82	$218.80	$218.80
Purchase #2	$204.43	5.435%	$215.5408	$215.54	$215.55	$215.50
Purchase #3	$75.28	5.103%	$79.1215	$79.12	$79.10	$79.10
Purchase #4	$81.76	9.485%	$89.5149	$89.51	$89.50	$89.50
Purchase #5	$129.98	7.451%	$139.6648	$139.66	$139.65	$139.70
Purchase #6	$210.71	13.654%	$239.4803	$239.48	$239.50	$239.50
Purchase #7	$94.34	11.321%	$105.0202	$105.02	$105.00	$105.00
7 purchase totals =	$1,001.39		$1,087.1671	$1,087.15	$1,087.10	$1,087.10