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	$30.27	13.715%	$34.4215	$34.42	$34.40	$34.40
Purchase #2	$174.94	6.458%	$186.2376	$186.24	$186.25	$186.20
Purchase #3	$44.48	5.855%	$47.0843	$47.08	$47.10	$47.10
Purchase #4	$85.42	3.166%	$88.1244	$88.12	$88.10	$88.10
Purchase #5	$213.25	12.472%	$239.8465	$239.85	$239.85	$239.80
Purchase #6	$37.72	12.622%	$42.481	$42.48	$42.50	$42.50
Purchase #7	$151.83	8.104%	$164.1343	$164.13	$164.15	$164.10
7 purchase totals =	$737.91		$802.3296	$802.32	$802.35	$802.20