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	$59.43	13.625%	$67.5273	$67.53	$67.55	$67.50
Purchase #2	$13.50	10.216%	$14.8792	$14.88	$14.90	$14.90
Purchase #3	$235.85	6.552%	$251.3029	$251.30	$251.30	$251.30
Purchase #4	$131.51	9.571%	$144.0968	$144.10	$144.10	$144.10
Purchase #5	$13.98	7.770%	$15.0662	$15.07	$15.05	$15.10
Purchase #6	$29.71	5.675%	$31.396	$31.40	$31.40	$31.40
Purchase #7	$57.25	4.791%	$59.9928	$59.99	$60.00	$60.00
7 purchase totals =	$541.23		$584.2612	$584.27	$584.30	$584.30