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	$45.88	9.712%	$50.3359	$50.34	$50.35	$50.30
Purchase #2	$49.46	5.149%	$52.0067	$52.01	$52.00	$52.00
Purchase #3	$66.89	10.405%	$73.8499	$73.85	$73.85	$73.80
Purchase #4	$188.71	8.119%	$204.0314	$204.03	$204.05	$204.00
Purchase #5	$38.79	4.628%	$40.5852	$40.59	$40.60	$40.60
Purchase #6	$60.83	5.713%	$64.3052	$64.31	$64.30	$64.30
Purchase #7	$149.57	12.375%	$168.0793	$168.08	$168.10	$168.10
7 purchase totals =	$600.13		$653.1936	$653.21	$653.25	$653.10