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	$127.79	3.232%	$131.9202	$131.92	$131.90	$131.90
Purchase #2	$185.59	13.720%	$211.0529	$211.05	$211.05	$211.10
Purchase #3	$149.36	12.767%	$168.4288	$168.43	$168.45	$168.40
Purchase #4	$108.85	13.567%	$123.6177	$123.62	$123.60	$123.60
Purchase #5	$183.89	3.268%	$189.8995	$189.90	$189.90	$189.90
Purchase #6	$108.28	12.334%	$121.6353	$121.64	$121.65	$121.60
Purchase #7	$46.89	5.186%	$49.3217	$49.32	$49.30	$49.30
7 purchase totals =	$910.65		$995.8761	$995.88	$995.85	$995.80