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	$82.50	5.118%	$86.7224	$86.72	$86.70	$86.70
Purchase #2	$118.25	4.493%	$123.563	$123.56	$123.55	$123.60
Purchase #3	$148.89	6.334%	$158.3207	$158.32	$158.30	$158.30
Purchase #4	$87.26	3.299%	$90.1387	$90.14	$90.15	$90.10
Purchase #5	$67.50	11.828%	$75.4839	$75.48	$75.50	$75.50
Purchase #6	$122.54	3.671%	$127.0384	$127.04	$127.05	$127.00
Purchase #7	$17.79	10.252%	$19.6138	$19.61	$19.60	$19.60
7 purchase totals =	$644.73		$680.8809	$680.87	$680.85	$680.80