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	$28.45	10.321%	$31.3863	$31.39	$31.40	$31.40
Purchase #2	$31.32	7.240%	$33.5876	$33.59	$33.60	$33.60
Purchase #3	$156.65	8.445%	$169.8791	$169.88	$169.90	$169.90
Purchase #4	$168.78	7.186%	$180.9085	$180.91	$180.90	$180.90
Purchase #5	$30.31	5.699%	$32.0374	$32.04	$32.05	$32.00
Purchase #6	$117.61	4.647%	$123.0753	$123.08	$123.10	$123.10
Purchase #7	$105.84	12.394%	$118.9578	$118.96	$118.95	$119.00
7 purchase totals =	$638.96		$689.8320	$689.85	$689.90	$689.90