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	$56.89	5.435%	$59.982	$59.98	$60.00	$60.00
Purchase #2	$211.52	10.408%	$233.535	$233.54	$233.55	$233.50
Purchase #3	$13.35	3.794%	$13.8565	$13.86	$13.85	$13.90
Purchase #4	$186.49	10.166%	$205.4486	$205.45	$205.45	$205.40
Purchase #5	$179.62	3.724%	$186.309	$186.31	$186.30	$186.30
Purchase #6	$80.96	9.377%	$88.5516	$88.55	$88.55	$88.60
Purchase #7	$32.47	12.577%	$36.5538	$36.55	$36.55	$36.60
7 purchase totals =	$761.30		$824.2365	$824.24	$824.25	$824.30