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	$75.53	6.620%	$80.5301	$80.53	$80.55	$80.50
Purchase #2	$244.90	4.637%	$256.256	$256.26	$256.25	$256.30
Purchase #3	$69.71	10.569%	$77.0776	$77.08	$77.10	$77.10
Purchase #4	$100.78	11.394%	$112.2629	$112.26	$112.25	$112.30
Purchase #5	$238.94	7.366%	$256.5403	$256.54	$256.55	$256.50
Purchase #6	$99.52	5.801%	$105.2932	$105.29	$105.30	$105.30
Purchase #7	$207.33	3.611%	$214.8167	$214.82	$214.80	$214.80
7 purchase totals =	$1,036.71		$1,102.7768	$1,102.78	$1,102.80	$1,102.80