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	$45.64	10.722%	$50.5335	$50.53	$50.55	$50.50
Purchase #2	$187.89	13.456%	$213.1725	$213.17	$213.15	$213.20
Purchase #3	$46.81	9.363%	$51.1928	$51.19	$51.20	$51.20
Purchase #4	$77.72	12.413%	$87.3674	$87.37	$87.35	$87.40
Purchase #5	$17.80	13.853%	$20.2658	$20.27	$20.25	$20.30
Purchase #6	$208.29	7.325%	$223.5472	$223.55	$223.55	$223.50
Purchase #7	$39.66	4.300%	$41.3654	$41.37	$41.35	$41.40
7 purchase totals =	$623.81		$687.4446	$687.45	$687.40	$687.50