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	$22.45	12.766%	$25.316	$25.32	$25.30	$25.30
Purchase #2	$136.92	5.625%	$144.6218	$144.62	$144.60	$144.60
Purchase #3	$39.70	13.162%	$44.9253	$44.93	$44.95	$44.90
Purchase #4	$229.69	6.790%	$245.286	$245.29	$245.30	$245.30
Purchase #5	$105.60	5.224%	$111.1165	$111.12	$111.10	$111.10
Purchase #6	$150.35	11.563%	$167.735	$167.74	$167.75	$167.70
Purchase #7	$80.35	5.868%	$85.0649	$85.06	$85.05	$85.10
7 purchase totals =	$765.06		$824.0655	$824.08	$824.05	$824.00