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	$245.61	10.670%	$271.8166	$271.82	$271.80	$271.80
Purchase #2	$133.90	6.452%	$142.5392	$142.54	$142.55	$142.50
Purchase #3	$123.54	11.338%	$137.547	$137.55	$137.55	$137.50
Purchase #4	$211.74	3.248%	$218.6173	$218.62	$218.60	$218.60
Purchase #5	$11.66	7.557%	$12.5411	$12.54	$12.55	$12.50
Purchase #6	$52.68	13.580%	$59.8339	$59.83	$59.85	$59.80
Purchase #7	$151.42	8.625%	$164.48	$164.48	$164.50	$164.50
7 purchase totals =	$930.55		$1,007.3751	$1,007.38	$1,007.40	$1,007.20