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	$82.39	10.488%	$91.0311	$91.03	$91.05	$91.00
Purchase #2	$144.28	4.268%	$150.4379	$150.44	$150.45	$150.40
Purchase #3	$57.35	12.591%	$64.5709	$64.57	$64.55	$64.60
Purchase #4	$46.56	11.390%	$51.8632	$51.86	$51.85	$51.90
Purchase #5	$35.25	7.226%	$37.7972	$37.80	$37.80	$37.80
Purchase #6	$142.51	10.465%	$157.4237	$157.42	$157.40	$157.40
Purchase #7	$10.92	5.139%	$11.4812	$11.48	$11.50	$11.50
7 purchase totals =	$519.26		$564.6052	$564.60	$564.60	$564.60