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	$136.36	13.835%	$155.2254	$155.23	$155.25	$155.20
Purchase #2	$56.90	3.438%	$58.8562	$58.86	$58.85	$58.90
Purchase #3	$77.56	9.619%	$85.0205	$85.02	$85.00	$85.00
Purchase #4	$57.60	6.480%	$61.3325	$61.33	$61.35	$61.30
Purchase #5	$40.85	3.843%	$42.4199	$42.42	$42.40	$42.40
Purchase #6	$227.87	12.535%	$256.4335	$256.43	$256.45	$256.40
Purchase #7	$20.29	4.131%	$21.1282	$21.13	$21.15	$21.10
7 purchase totals =	$617.43		$680.4162	$680.42	$680.45	$680.30