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	$77.76	9.408%	$85.0757	$85.08	$85.10	$85.10
Purchase #2	$94.49	11.800%	$105.6398	$105.64	$105.65	$105.60
Purchase #3	$117.86	8.832%	$128.2694	$128.27	$128.25	$128.30
Purchase #4	$104.65	4.703%	$109.5717	$109.57	$109.55	$109.60
Purchase #5	$134.57	13.796%	$153.1353	$153.14	$153.15	$153.10
Purchase #6	$90.33	6.674%	$96.3586	$96.36	$96.35	$96.40
Purchase #7	$234.90	11.834%	$262.6981	$262.70	$262.70	$262.70
7 purchase totals =	$854.56		$940.7486	$940.76	$940.75	$940.80