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	$239.57	9.210%	$261.6344	$261.63	$261.65	$261.60
Purchase #2	$247.95	4.388%	$258.83	$258.83	$258.85	$258.80
Purchase #3	$108.39	6.798%	$115.7584	$115.76	$115.75	$115.80
Purchase #4	$98.62	8.831%	$107.3291	$107.33	$107.35	$107.30
Purchase #5	$102.52	8.709%	$111.4485	$111.45	$111.45	$111.40
Purchase #6	$119.73	9.496%	$131.0996	$131.10	$131.10	$131.10
Purchase #7	$98.82	12.263%	$110.9383	$110.94	$110.95	$110.90
7 purchase totals =	$1,015.60		$1,097.0383	$1,097.04	$1,097.10	$1,096.90