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	$124.54	12.322%	$139.8858	$139.89	$139.90	$139.90
Purchase #2	$106.66	6.415%	$113.5022	$113.50	$113.50	$113.50
Purchase #3	$13.56	10.244%	$14.9491	$14.95	$14.95	$14.90
Purchase #4	$246.35	9.637%	$270.0907	$270.09	$270.10	$270.10
Purchase #5	$175.86	4.393%	$183.5855	$183.59	$183.60	$183.60
Purchase #6	$167.35	10.310%	$184.6038	$184.60	$184.60	$184.60
Purchase #7	$133.40	12.836%	$150.5232	$150.52	$150.50	$150.50
7 purchase totals =	$967.72		$1,057.1403	$1,057.14	$1,057.15	$1,057.10