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	$50.39	7.746%	$54.2932	$54.29	$54.30	$54.30
Purchase #2	$97.46	6.203%	$103.5054	$103.51	$103.50	$103.50
Purchase #3	$210.30	12.464%	$236.5118	$236.51	$236.50	$236.50
Purchase #4	$186.32	6.242%	$197.9501	$197.95	$197.95	$198.00
Purchase #5	$71.69	9.392%	$78.4231	$78.42	$78.40	$78.40
Purchase #6	$223.85	8.195%	$242.1945	$242.19	$242.20	$242.20
Purchase #7	$176.48	5.521%	$186.2235	$186.22	$186.20	$186.20
7 purchase totals =	$1,016.49		$1,099.1016	$1,099.09	$1,099.05	$1,099.10