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	$249.93	4.365%	$260.8394	$260.84	$260.85	$260.80
Purchase #2	$74.85	10.372%	$82.6134	$82.61	$82.60	$82.60
Purchase #3	$142.43	11.271%	$158.4833	$158.48	$158.50	$158.50
Purchase #4	$99.39	4.181%	$103.5455	$103.55	$103.55	$103.50
Purchase #5	$39.40	12.536%	$44.3392	$44.34	$44.35	$44.30
Purchase #6	$84.56	4.241%	$88.1462	$88.15	$88.15	$88.10
Purchase #7	$132.72	3.282%	$137.0759	$137.08	$137.10	$137.10
7 purchase totals =	$823.28		$875.0429	$875.05	$875.10	$874.90