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	$138.60	12.236%	$155.5591	$155.56	$155.55	$155.60
Purchase #2	$156.55	8.159%	$169.3229	$169.32	$169.30	$169.30
Purchase #3	$144.26	4.812%	$151.2018	$151.20	$151.20	$151.20
Purchase #4	$18.79	10.854%	$20.8295	$20.83	$20.85	$20.80
Purchase #5	$103.42	6.273%	$109.9075	$109.91	$109.90	$109.90
Purchase #6	$33.99	11.435%	$37.8768	$37.88	$37.90	$37.90
Purchase #7	$178.64	13.527%	$202.8046	$202.80	$202.80	$202.80
7 purchase totals =	$774.25		$847.5022	$847.50	$847.50	$847.50