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	$43.75	11.302%	$48.6946	$48.69	$48.70	$48.70
Purchase #2	$75.38	3.628%	$78.1148	$78.11	$78.10	$78.10
Purchase #3	$224.66	3.487%	$232.4939	$232.49	$232.50	$232.50
Purchase #4	$96.31	9.507%	$105.4662	$105.47	$105.45	$105.50
Purchase #5	$237.90	7.123%	$254.8456	$254.85	$254.85	$254.80
Purchase #6	$14.43	8.390%	$15.6407	$15.64	$15.65	$15.60
Purchase #7	$243.85	4.605%	$255.0793	$255.08	$255.10	$255.10
7 purchase totals =	$936.28		$990.3351	$990.33	$990.35	$990.30