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	$27.42	6.121%	$29.0984	$29.10	$29.10	$29.10
Purchase #2	$78.25	5.624%	$82.6508	$82.65	$82.65	$82.70
Purchase #3	$99.58	6.312%	$105.8655	$105.87	$105.85	$105.90
Purchase #4	$69.49	13.132%	$78.6154	$78.62	$78.60	$78.60
Purchase #5	$28.39	8.767%	$30.879	$30.88	$30.90	$30.90
Purchase #6	$151.57	6.260%	$161.0583	$161.06	$161.05	$161.10
Purchase #7	$185.60	3.496%	$192.0886	$192.09	$192.10	$192.10
7 purchase totals =	$640.30		$680.2560	$680.27	$680.25	$680.40