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	$146.81	13.436%	$166.5354	$166.54	$166.55	$166.50
Purchase #2	$133.90	4.483%	$139.9027	$139.90	$139.90	$139.90
Purchase #3	$71.49	13.651%	$81.2491	$81.25	$81.25	$81.20
Purchase #4	$7.45	3.849%	$7.7368	$7.74	$7.75	$7.70
Purchase #5	$56.60	5.217%	$59.5528	$59.55	$59.55	$59.60
Purchase #6	$248.71	11.391%	$277.0406	$277.04	$277.05	$277.00
Purchase #7	$118.32	12.821%	$133.4898	$133.49	$133.50	$133.50
7 purchase totals =	$783.28		$865.5072	$865.51	$865.55	$865.40