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	$234.35	10.575%	$259.1325	$259.13	$259.15	$259.10
Purchase #2	$90.25	12.502%	$101.5331	$101.53	$101.55	$101.50
Purchase #3	$139.94	4.844%	$146.7187	$146.72	$146.70	$146.70
Purchase #4	$32.41	4.496%	$33.8672	$33.87	$33.85	$33.90
Purchase #5	$83.48	5.328%	$87.9278	$87.93	$87.95	$87.90
Purchase #6	$63.89	10.321%	$70.4841	$70.48	$70.50	$70.50
Purchase #7	$177.77	12.688%	$200.3255	$200.33	$200.35	$200.30
7 purchase totals =	$822.09		$899.9889	$899.99	$900.05	$899.90