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	$221.60	5.790%	$234.4306	$234.43	$234.45	$234.40
Purchase #2	$51.59	10.267%	$56.8867	$56.89	$56.90	$56.90
Purchase #3	$241.55	5.827%	$255.6251	$255.63	$255.65	$255.60
Purchase #4	$184.48	8.409%	$199.9929	$199.99	$200.00	$200.00
Purchase #5	$130.40	11.855%	$145.8589	$145.86	$145.85	$145.90
Purchase #6	$75.46	13.328%	$85.5173	$85.52	$85.50	$85.50
Purchase #7	$238.95	12.278%	$268.2883	$268.29	$268.30	$268.30
7 purchase totals =	$1,144.03		$1,246.5998	$1,246.61	$1,246.65	$1,246.60