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	$122.79	13.619%	$139.5128	$139.51	$139.50	$139.50
Purchase #2	$244.89	7.552%	$263.3841	$263.38	$263.40	$263.40
Purchase #3	$250.87	13.874%	$285.6757	$285.68	$285.70	$285.70
Purchase #4	$220.46	3.106%	$227.3075	$227.31	$227.30	$227.30
Purchase #5	$101.63	4.791%	$106.4991	$106.50	$106.50	$106.50
Purchase #6	$40.43	3.522%	$41.8539	$41.85	$41.85	$41.90
Purchase #7	$78.43	12.758%	$88.4361	$88.44	$88.45	$88.40
7 purchase totals =	$1,059.50		$1,152.6692	$1,152.67	$1,152.70	$1,152.70