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	$30.28	5.221%	$31.8609	$31.86	$31.85	$31.90
Purchase #2	$186.82	4.800%	$195.7874	$195.79	$195.80	$195.80
Purchase #3	$133.84	6.168%	$142.0953	$142.10	$142.10	$142.10
Purchase #4	$42.78	6.636%	$45.6189	$45.62	$45.60	$45.60
Purchase #5	$173.51	9.729%	$190.3908	$190.39	$190.40	$190.40
Purchase #6	$45.48	8.553%	$49.3699	$49.37	$49.35	$49.40
Purchase #7	$135.96	5.314%	$143.1849	$143.18	$143.20	$143.20
7 purchase totals =	$748.67		$798.3081	$798.31	$798.30	$798.40