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	$146.96	13.210%	$166.3734	$166.37	$166.35	$166.40
Purchase #2	$46.74	3.666%	$48.4535	$48.45	$48.45	$48.50
Purchase #3	$140.62	7.817%	$151.6123	$151.61	$151.60	$151.60
Purchase #4	$114.93	4.672%	$120.2995	$120.30	$120.30	$120.30
Purchase #5	$124.35	6.850%	$132.868	$132.87	$132.85	$132.90
Purchase #6	$250.58	12.466%	$281.8173	$281.82	$281.80	$281.80
Purchase #7	$94.75	9.178%	$103.4462	$103.45	$103.45	$103.40
7 purchase totals =	$918.93		$1,004.8702	$1,004.87	$1,004.80	$1,004.90