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	$249.49	6.780%	$266.4054	$266.41	$266.40	$266.40
Purchase #2	$95.69	3.501%	$99.0401	$99.04	$99.05	$99.00
Purchase #3	$34.65	9.222%	$37.8454	$37.85	$37.85	$37.80
Purchase #4	$158.53	5.782%	$167.6962	$167.70	$167.70	$167.70
Purchase #5	$43.31	9.504%	$47.4262	$47.43	$47.45	$47.40
Purchase #6	$182.25	12.637%	$205.2809	$205.28	$205.30	$205.30
Purchase #7	$240.38	6.153%	$255.1706	$255.17	$255.15	$255.20
7 purchase totals =	$1,004.30		$1,078.8648	$1,078.88	$1,078.90	$1,078.80