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	$139.67	4.478%	$145.9244	$145.92	$145.90	$145.90
Purchase #2	$113.83	12.756%	$128.3502	$128.35	$128.35	$128.40
Purchase #3	$143.40	3.819%	$148.8764	$148.88	$148.90	$148.90
Purchase #4	$86.58	4.641%	$90.5982	$90.60	$90.60	$90.60
Purchase #5	$235.65	4.661%	$246.6336	$246.63	$246.65	$246.60
Purchase #6	$184.39	10.451%	$203.6606	$203.66	$203.65	$203.70
Purchase #7	$67.44	13.363%	$76.452	$76.45	$76.45	$76.50
7 purchase totals =	$970.96		$1,040.4954	$1,040.49	$1,040.50	$1,040.60