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	$86.46	9.460%	$94.6391	$94.64	$94.65	$94.60
Purchase #2	$117.83	8.150%	$127.4331	$127.43	$127.45	$127.40
Purchase #3	$175.35	13.111%	$198.3401	$198.34	$198.35	$198.30
Purchase #4	$124.34	9.590%	$136.2642	$136.26	$136.25	$136.30
Purchase #5	$76.29	12.475%	$85.8072	$85.81	$85.80	$85.80
Purchase #6	$87.31	10.632%	$96.5928	$96.59	$96.60	$96.60
Purchase #7	$91.59	13.564%	$104.0133	$104.01	$104.00	$104.00
7 purchase totals =	$759.17		$843.0898	$843.08	$843.10	$843.00