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	$100.47	7.515%	$108.0203	$108.02	$108.00	$108.00
Purchase #2	$132.59	7.866%	$143.0195	$143.02	$143.00	$143.00
Purchase #3	$249.73	13.824%	$284.2527	$284.25	$284.25	$284.30
Purchase #4	$76.63	7.784%	$82.5949	$82.59	$82.60	$82.60
Purchase #5	$89.79	5.137%	$94.4025	$94.40	$94.40	$94.40
Purchase #6	$112.48	13.373%	$127.522	$127.52	$127.50	$127.50
Purchase #7	$87.80	3.360%	$90.7501	$90.75	$90.75	$90.80
7 purchase totals =	$849.49		$930.5620	$930.55	$930.50	$930.60