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	$166.72	7.861%	$179.8259	$179.83	$179.85	$179.80
Purchase #2	$37.77	12.397%	$42.4523	$42.45	$42.45	$42.50
Purchase #3	$133.37	6.586%	$142.1537	$142.15	$142.15	$142.20
Purchase #4	$43.51	11.159%	$48.3653	$48.37	$48.35	$48.40
Purchase #5	$40.63	7.111%	$43.5192	$43.52	$43.50	$43.50
Purchase #6	$63.91	11.606%	$71.3274	$71.33	$71.35	$71.30
Purchase #7	$132.89	13.465%	$150.7836	$150.78	$150.80	$150.80
7 purchase totals =	$618.80		$678.4274	$678.43	$678.45	$678.50