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	$236.70	4.811%	$248.0876	$248.09	$248.10	$248.10
Purchase #2	$94.62	6.160%	$100.4486	$100.45	$100.45	$100.40
Purchase #3	$102.90	5.464%	$108.5225	$108.52	$108.50	$108.50
Purchase #4	$226.27	11.121%	$251.4335	$251.43	$251.45	$251.40
Purchase #5	$53.59	5.342%	$56.4528	$56.45	$56.45	$56.50
Purchase #6	$123.54	13.571%	$140.3056	$140.31	$140.30	$140.30
Purchase #7	$86.39	8.231%	$93.5008	$93.50	$93.50	$93.50
7 purchase totals =	$924.01		$998.7514	$998.75	$998.75	$998.70