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	$185.36	12.570%	$208.6598	$208.66	$208.65	$208.70
Purchase #2	$16.95	9.197%	$18.5089	$18.51	$18.50	$18.50
Purchase #3	$127.87	3.626%	$132.5066	$132.51	$132.50	$132.50
Purchase #4	$155.25	3.661%	$160.9337	$160.93	$160.95	$160.90
Purchase #5	$117.72	9.194%	$128.5432	$128.54	$128.55	$128.50
Purchase #6	$54.42	12.728%	$61.3466	$61.35	$61.35	$61.30
Purchase #7	$96.25	8.282%	$104.2214	$104.22	$104.20	$104.20
7 purchase totals =	$753.82		$814.7202	$814.72	$814.70	$814.60