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	$54.35	11.865%	$60.7986	$60.80	$60.80	$60.80
Purchase #2	$200.43	11.189%	$222.8561	$222.86	$222.85	$222.90
Purchase #3	$132.95	13.695%	$151.1575	$151.16	$151.15	$151.20
Purchase #4	$19.26	13.129%	$21.7886	$21.79	$21.80	$21.80
Purchase #5	$76.87	4.806%	$80.5644	$80.56	$80.55	$80.60
Purchase #6	$66.59	9.352%	$72.8175	$72.82	$72.80	$72.80
Purchase #7	$61.46	10.583%	$67.9643	$67.96	$67.95	$68.00
7 purchase totals =	$611.91		$677.9470	$677.95	$677.90	$678.10