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	$55.32	7.316%	$59.3672	$59.37	$59.35	$59.40
Purchase #2	$160.85	12.536%	$181.0142	$181.01	$181.00	$181.00
Purchase #3	$54.96	5.260%	$57.8509	$57.85	$57.85	$57.90
Purchase #4	$140.49	5.642%	$148.4164	$148.42	$148.40	$148.40
Purchase #5	$172.30	4.854%	$180.6634	$180.66	$180.65	$180.70
Purchase #6	$13.97	9.857%	$15.347	$15.35	$15.35	$15.30
Purchase #7	$168.26	8.710%	$182.9154	$182.92	$182.90	$182.90
7 purchase totals =	$766.15		$825.5745	$825.58	$825.50	$825.60