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	$129.72	9.866%	$142.5182	$142.52	$142.50	$142.50
Purchase #2	$185.90	6.109%	$197.2566	$197.26	$197.25	$197.30
Purchase #3	$117.25	11.421%	$130.6411	$130.64	$130.65	$130.60
Purchase #4	$86.93	9.739%	$95.3961	$95.40	$95.40	$95.40
Purchase #5	$231.87	10.792%	$256.8934	$256.89	$256.90	$256.90
Purchase #6	$182.82	4.159%	$190.4235	$190.42	$190.40	$190.40
Purchase #7	$155.80	13.554%	$176.9171	$176.92	$176.90	$176.90
7 purchase totals =	$1,090.29		$1,190.0460	$1,190.05	$1,190.00	$1,190.00