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	$139.75	5.129%	$146.9178	$146.92	$146.90	$146.90
Purchase #2	$97.28	11.192%	$108.1676	$108.17	$108.15	$108.20
Purchase #3	$43.43	11.137%	$48.2668	$48.27	$48.25	$48.30
Purchase #4	$111.30	5.440%	$117.3547	$117.35	$117.35	$117.40
Purchase #5	$41.81	10.676%	$46.2736	$46.27	$46.25	$46.30
Purchase #6	$114.69	7.492%	$123.2826	$123.28	$123.30	$123.30
Purchase #7	$13.32	10.246%	$14.6848	$14.68	$14.70	$14.70
7 purchase totals =	$561.58		$604.9479	$604.94	$604.90	$605.10