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	$37.28	8.869%	$40.5864	$40.59	$40.60	$40.60
Purchase #2	$42.74	12.234%	$47.9688	$47.97	$47.95	$48.00
Purchase #3	$33.40	12.696%	$37.6405	$37.64	$37.65	$37.60
Purchase #4	$223.91	4.493%	$233.9703	$233.97	$233.95	$234.00
Purchase #5	$135.76	5.192%	$142.8087	$142.81	$142.80	$142.80
Purchase #6	$150.73	12.315%	$169.2924	$169.29	$169.30	$169.30
Purchase #7	$11.25	8.831%	$12.2435	$12.24	$12.25	$12.20
7 purchase totals =	$635.07		$684.5106	$684.51	$684.50	$684.50