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	$125.32	9.178%	$136.8219	$136.82	$136.80	$136.80
Purchase #2	$105.48	10.858%	$116.933	$116.93	$116.95	$116.90
Purchase #3	$127.35	11.762%	$142.3289	$142.33	$142.35	$142.30
Purchase #4	$38.76	12.694%	$43.6802	$43.68	$43.70	$43.70
Purchase #5	$131.27	7.630%	$141.2859	$141.29	$141.30	$141.30
Purchase #6	$198.68	8.646%	$215.8579	$215.86	$215.85	$215.90
Purchase #7	$116.51	11.497%	$129.9052	$129.91	$129.90	$129.90
7 purchase totals =	$843.37		$926.8130	$926.82	$926.85	$926.80