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	$145.42	6.113%	$154.3095	$154.31	$154.30	$154.30
Purchase #2	$63.85	12.807%	$72.0273	$72.03	$72.05	$72.00
Purchase #3	$64.41	9.705%	$70.661	$70.66	$70.65	$70.70
Purchase #4	$34.74	4.730%	$36.3832	$36.38	$36.40	$36.40
Purchase #5	$66.37	8.305%	$71.882	$71.88	$71.90	$71.90
Purchase #6	$93.60	9.436%	$102.4321	$102.43	$102.45	$102.40
Purchase #7	$105.28	7.484%	$113.1592	$113.16	$113.15	$113.20
7 purchase totals =	$573.67		$620.8543	$620.85	$620.90	$620.90