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	$30.41	12.697%	$34.2712	$34.27	$34.25	$34.30
Purchase #2	$31.49	3.223%	$32.5049	$32.50	$32.50	$32.50
Purchase #3	$81.59	10.163%	$89.882	$89.88	$89.90	$89.90
Purchase #4	$51.25	4.141%	$53.3723	$53.37	$53.35	$53.40
Purchase #5	$115.66	4.303%	$120.6368	$120.64	$120.65	$120.60
Purchase #6	$221.42	13.756%	$251.8785	$251.88	$251.90	$251.90
Purchase #7	$38.89	7.169%	$41.678	$41.68	$41.70	$41.70
7 purchase totals =	$570.71		$624.2237	$624.22	$624.25	$624.30