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	$139.29	3.643%	$144.3643	$144.36	$144.35	$144.40
Purchase #2	$177.70	11.283%	$197.7499	$197.75	$197.75	$197.70
Purchase #3	$40.62	7.434%	$43.6397	$43.64	$43.65	$43.60
Purchase #4	$91.43	9.856%	$100.4413	$100.44	$100.45	$100.40
Purchase #5	$85.25	12.209%	$95.6582	$95.66	$95.65	$95.70
Purchase #6	$37.63	12.803%	$42.4478	$42.45	$42.45	$42.40
Purchase #7	$236.32	12.439%	$265.7158	$265.72	$265.70	$265.70
7 purchase totals =	$808.24		$890.0170	$890.02	$890.00	$889.90