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	$47.25	6.786%	$50.4564	$50.46	$50.45	$50.50
Purchase #2	$17.69	13.345%	$20.0507	$20.05	$20.05	$20.10
Purchase #3	$23.54	12.508%	$26.4844	$26.48	$26.50	$26.50
Purchase #4	$89.64	8.738%	$97.4727	$97.47	$97.45	$97.50
Purchase #5	$139.30	11.335%	$155.0897	$155.09	$155.10	$155.10
Purchase #6	$79.85	13.180%	$90.3742	$90.37	$90.35	$90.40
Purchase #7	$192.76	3.374%	$199.2637	$199.26	$199.25	$199.30
7 purchase totals =	$590.03		$639.1918	$639.18	$639.15	$639.40