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	$147.86	13.806%	$168.2736	$168.27	$168.25	$168.30
Purchase #2	$76.74	12.836%	$86.5903	$86.59	$86.60	$86.60
Purchase #3	$90.98	9.350%	$99.4866	$99.49	$99.50	$99.50
Purchase #4	$231.67	12.480%	$260.5824	$260.58	$260.60	$260.60
Purchase #5	$179.62	10.516%	$198.5088	$198.51	$198.50	$198.50
Purchase #6	$86.29	4.453%	$90.1325	$90.13	$90.15	$90.10
Purchase #7	$238.95	3.338%	$246.9262	$246.93	$246.95	$246.90
7 purchase totals =	$1,052.11		$1,150.5004	$1,150.50	$1,150.55	$1,150.50