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	$120.61	9.848%	$132.4877	$132.49	$132.50	$132.50
Purchase #2	$40.70	6.866%	$43.4945	$43.49	$43.50	$43.50
Purchase #3	$85.46	7.768%	$92.0985	$92.10	$92.10	$92.10
Purchase #4	$60.85	11.666%	$67.9488	$67.95	$67.95	$67.90
Purchase #5	$43.82	6.689%	$46.7511	$46.75	$46.75	$46.80
Purchase #6	$14.28	5.346%	$15.0434	$15.04	$15.05	$15.00
Purchase #7	$234.97	3.582%	$243.3866	$243.39	$243.40	$243.40
7 purchase totals =	$600.69		$641.2106	$641.21	$641.25	$641.20