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	$67.73	4.141%	$70.5347	$70.53	$70.55	$70.50
Purchase #2	$190.91	13.636%	$216.9425	$216.94	$216.95	$216.90
Purchase #3	$124.33	3.477%	$128.653	$128.65	$128.65	$128.70
Purchase #4	$60.85	5.613%	$64.2655	$64.27	$64.25	$64.30
Purchase #5	$44.25	5.770%	$46.8032	$46.80	$46.80	$46.80
Purchase #6	$151.43	8.848%	$164.8285	$164.83	$164.85	$164.80
Purchase #7	$123.54	3.557%	$127.9343	$127.93	$127.95	$127.90
7 purchase totals =	$763.04		$819.9617	$819.95	$820.00	$819.90