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	$153.98	6.693%	$164.2859	$164.29	$164.30	$164.30
Purchase #2	$199.89	7.625%	$215.1316	$215.13	$215.15	$215.10
Purchase #3	$43.37	12.566%	$48.8199	$48.82	$48.80	$48.80
Purchase #4	$26.48	5.167%	$27.8482	$27.85	$27.85	$27.80
Purchase #5	$72.27	10.541%	$79.888	$79.89	$79.90	$79.90
Purchase #6	$239.47	13.642%	$272.1385	$272.14	$272.15	$272.10
Purchase #7	$73.79	11.257%	$82.0965	$82.10	$82.10	$82.10
7 purchase totals =	$809.25		$890.2086	$890.22	$890.25	$890.10