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	$133.61	7.319%	$143.3889	$143.39	$143.40	$143.40
Purchase #2	$69.58	13.203%	$78.7666	$78.77	$78.75	$78.80
Purchase #3	$108.42	13.681%	$123.2529	$123.25	$123.25	$123.30
Purchase #4	$127.34	9.459%	$139.3851	$139.39	$139.40	$139.40
Purchase #5	$166.36	5.331%	$175.2287	$175.23	$175.25	$175.20
Purchase #6	$140.98	7.826%	$152.0131	$152.01	$152.00	$152.00
Purchase #7	$248.79	12.374%	$279.5753	$279.58	$279.60	$279.60
7 purchase totals =	$995.08		$1,091.6106	$1,091.62	$1,091.65	$1,091.70