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	$137.87	13.765%	$156.8478	$156.85	$156.85	$156.80
Purchase #2	$126.45	8.807%	$137.5865	$137.59	$137.60	$137.60
Purchase #3	$39.96	13.839%	$45.4901	$45.49	$45.50	$45.50
Purchase #4	$165.72	4.527%	$173.2221	$173.22	$173.20	$173.20
Purchase #5	$84.79	13.220%	$95.9992	$96.00	$96.00	$96.00
Purchase #6	$73.96	12.680%	$83.3381	$83.34	$83.35	$83.30
Purchase #7	$236.34	4.861%	$247.8285	$247.83	$247.85	$247.80
7 purchase totals =	$865.09		$940.3123	$940.32	$940.35	$940.20