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	$90.69	10.861%	$100.5398	$100.54	$100.55	$100.50
Purchase #2	$143.66	5.474%	$151.5239	$151.52	$151.50	$151.50
Purchase #3	$179.83	9.273%	$196.5056	$196.51	$196.50	$196.50
Purchase #4	$250.64	11.635%	$279.802	$279.80	$279.80	$279.80
Purchase #5	$203.96	10.820%	$226.0285	$226.03	$226.05	$226.00
Purchase #6	$247.74	11.759%	$276.8717	$276.87	$276.85	$276.90
Purchase #7	$120.41	6.564%	$128.3137	$128.31	$128.30	$128.30
7 purchase totals =	$1,236.93		$1,359.5852	$1,359.58	$1,359.55	$1,359.50