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	$27.25	9.583%	$29.8614	$29.86	$29.85	$29.90
Purchase #2	$93.47	6.724%	$99.7549	$99.75	$99.75	$99.80
Purchase #3	$205.97	4.424%	$215.0821	$215.08	$215.10	$215.10
Purchase #4	$96.44	8.804%	$104.9306	$104.93	$104.95	$104.90
Purchase #5	$81.70	6.253%	$86.8087	$86.81	$86.80	$86.80
Purchase #6	$185.81	5.647%	$196.3027	$196.30	$196.30	$196.30
Purchase #7	$235.60	10.280%	$259.8197	$259.82	$259.80	$259.80
7 purchase totals =	$926.24		$992.5601	$992.55	$992.55	$992.60