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	$154.70	11.839%	$173.0149	$173.01	$173.00	$173.00
Purchase #2	$127.88	7.193%	$137.0784	$137.08	$137.10	$137.10
Purchase #3	$70.98	10.336%	$78.3165	$78.32	$78.30	$78.30
Purchase #4	$76.46	11.375%	$85.1573	$85.16	$85.15	$85.20
Purchase #5	$65.72	6.372%	$69.9077	$69.91	$69.90	$69.90
Purchase #6	$157.60	5.580%	$166.3941	$166.39	$166.40	$166.40
Purchase #7	$201.75	4.652%	$211.1354	$211.14	$211.15	$211.10
7 purchase totals =	$855.09		$921.0043	$921.01	$921.00	$921.00