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	$156.49	12.691%	$176.3501	$176.35	$176.35	$176.40
Purchase #2	$46.87	12.634%	$52.7916	$52.79	$52.80	$52.80
Purchase #3	$183.49	9.128%	$200.239	$200.24	$200.25	$200.20
Purchase #4	$81.52	10.737%	$90.2728	$90.27	$90.25	$90.30
Purchase #5	$150.72	12.400%	$169.4093	$169.41	$169.40	$169.40
Purchase #6	$91.32	13.229%	$103.4007	$103.40	$103.40	$103.40
Purchase #7	$34.65	5.364%	$36.5086	$36.51	$36.50	$36.50
7 purchase totals =	$745.06		$828.9721	$828.97	$828.95	$829.00