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	$223.47	5.824%	$236.4849	$236.48	$236.50	$236.50
Purchase #2	$129.64	6.593%	$138.1872	$138.19	$138.20	$138.20
Purchase #3	$220.76	12.410%	$248.1563	$248.16	$248.15	$248.20
Purchase #4	$174.94	9.124%	$190.9015	$190.90	$190.90	$190.90
Purchase #5	$113.41	4.733%	$118.7777	$118.78	$118.80	$118.80
Purchase #6	$59.47	13.438%	$67.4616	$67.46	$67.45	$67.50
Purchase #7	$80.89	6.639%	$86.2603	$86.26	$86.25	$86.30
7 purchase totals =	$1,002.58		$1,086.2295	$1,086.23	$1,086.25	$1,086.40