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	$18.65	10.830%	$20.6698	$20.67	$20.65	$20.70
Purchase #2	$42.70	5.589%	$45.0865	$45.09	$45.10	$45.10
Purchase #3	$23.77	7.642%	$25.5865	$25.59	$25.60	$25.60
Purchase #4	$155.70	8.174%	$168.4269	$168.43	$168.45	$168.40
Purchase #5	$63.80	3.268%	$65.885	$65.89	$65.90	$65.90
Purchase #6	$151.66	5.561%	$160.0938	$160.09	$160.10	$160.10
Purchase #7	$211.68	3.465%	$219.0147	$219.01	$219.00	$219.00
7 purchase totals =	$667.96		$704.7632	$704.77	$704.80	$704.80