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	$83.71	6.804%	$89.4056	$89.41	$89.40	$89.40
Purchase #2	$177.42	4.188%	$184.8503	$184.85	$184.85	$184.90
Purchase #3	$249.56	12.750%	$281.3789	$281.38	$281.40	$281.40
Purchase #4	$9.31	3.119%	$9.6004	$9.60	$9.60	$9.60
Purchase #5	$168.51	4.642%	$176.3322	$176.33	$176.35	$176.30
Purchase #6	$85.83	13.642%	$97.5389	$97.54	$97.55	$97.50
Purchase #7	$120.69	9.754%	$132.4621	$132.46	$132.45	$132.50
7 purchase totals =	$895.03		$971.5684	$971.57	$971.60	$971.60