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	$54.38	6.347%	$57.8315	$57.83	$57.85	$57.80
Purchase #2	$147.50	13.510%	$167.4273	$167.43	$167.45	$167.40
Purchase #3	$59.83	13.209%	$67.7329	$67.73	$67.75	$67.70
Purchase #4	$126.36	13.813%	$143.8141	$143.81	$143.80	$143.80
Purchase #5	$91.67	3.301%	$94.696	$94.70	$94.70	$94.70
Purchase #6	$189.68	12.122%	$212.673	$212.67	$212.65	$212.70
Purchase #7	$40.85	11.602%	$45.5894	$45.59	$45.60	$45.60
7 purchase totals =	$710.27		$789.7642	$789.76	$789.80	$789.70