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	$247.60	3.575%	$256.4517	$256.45	$256.45	$256.50
Purchase #2	$183.51	9.153%	$200.3067	$200.31	$200.30	$200.30
Purchase #3	$7.65	11.238%	$8.5097	$8.51	$8.50	$8.50
Purchase #4	$82.99	4.763%	$86.9428	$86.94	$86.95	$86.90
Purchase #5	$33.52	11.800%	$37.4754	$37.48	$37.50	$37.50
Purchase #6	$123.85	13.296%	$140.3171	$140.32	$140.30	$140.30
Purchase #7	$94.79	4.102%	$98.6783	$98.68	$98.70	$98.70
7 purchase totals =	$773.91		$828.6817	$828.69	$828.70	$828.70