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	$188.95	11.111%	$209.9442	$209.94	$209.95	$209.90
Purchase #2	$73.58	9.234%	$80.3744	$80.37	$80.35	$80.40
Purchase #3	$99.89	7.200%	$107.0821	$107.08	$107.10	$107.10
Purchase #4	$151.31	13.408%	$171.5976	$171.60	$171.60	$171.60
Purchase #5	$133.52	4.432%	$139.4376	$139.44	$139.45	$139.40
Purchase #6	$153.76	7.848%	$165.8271	$165.83	$165.85	$165.80
Purchase #7	$94.61	6.247%	$100.5203	$100.52	$100.50	$100.50
7 purchase totals =	$895.62		$974.7833	$974.78	$974.80	$974.70