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	$39.34	6.503%	$41.8983	$41.90	$41.90	$41.90
Purchase #2	$234.52	5.509%	$247.4397	$247.44	$247.45	$247.40
Purchase #3	$95.98	3.714%	$99.5447	$99.54	$99.55	$99.50
Purchase #4	$168.80	10.378%	$186.3181	$186.32	$186.30	$186.30
Purchase #5	$216.48	4.128%	$225.4163	$225.42	$225.40	$225.40
Purchase #6	$138.88	6.750%	$148.2544	$148.25	$148.25	$148.30
Purchase #7	$24.58	12.521%	$27.6577	$27.66	$27.65	$27.70
7 purchase totals =	$918.58		$976.5292	$976.53	$976.50	$976.50