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	$83.54	6.555%	$89.016	$89.02	$89.00	$89.00
Purchase #2	$113.69	8.461%	$123.3093	$123.31	$123.30	$123.30
Purchase #3	$102.28	12.510%	$115.0752	$115.08	$115.10	$115.10
Purchase #4	$43.32	13.673%	$49.2431	$49.24	$49.25	$49.20
Purchase #5	$211.59	6.725%	$225.8194	$225.82	$225.80	$225.80
Purchase #6	$69.94	4.339%	$72.9747	$72.97	$72.95	$73.00
Purchase #7	$144.99	9.703%	$159.0584	$159.06	$159.05	$159.10
7 purchase totals =	$769.35		$834.4961	$834.50	$834.45	$834.50