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	$70.53	10.246%	$77.7565	$77.76	$77.75	$77.80
Purchase #2	$43.46	9.137%	$47.4309	$47.43	$47.45	$47.40
Purchase #3	$150.55	3.702%	$156.1234	$156.12	$156.10	$156.10
Purchase #4	$80.39	4.201%	$83.7672	$83.77	$83.75	$83.80
Purchase #5	$32.61	3.688%	$33.8127	$33.81	$33.80	$33.80
Purchase #6	$171.27	6.121%	$181.7534	$181.75	$181.75	$181.80
Purchase #7	$196.77	12.419%	$221.2069	$221.21	$221.20	$221.20
7 purchase totals =	$745.58		$801.8510	$801.85	$801.80	$801.90