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	$41.34	9.601%	$45.3091	$45.31	$45.30	$45.30
Purchase #2	$102.32	4.623%	$107.0503	$107.05	$107.05	$107.10
Purchase #3	$107.39	3.613%	$111.27	$111.27	$111.25	$111.30
Purchase #4	$160.71	11.320%	$178.9024	$178.90	$178.90	$178.90
Purchase #5	$194.89	11.788%	$217.8636	$217.86	$217.85	$217.90
Purchase #6	$146.62	9.766%	$160.9389	$160.94	$160.95	$160.90
Purchase #7	$94.62	5.792%	$100.1004	$100.10	$100.10	$100.10
7 purchase totals =	$847.89		$921.4347	$921.43	$921.40	$921.50