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	$242.94	11.591%	$271.0992	$271.10	$271.10	$271.10
Purchase #2	$145.47	6.850%	$155.4347	$155.43	$155.45	$155.40
Purchase #3	$139.47	11.490%	$155.4951	$155.50	$155.50	$155.50
Purchase #4	$196.32	12.624%	$221.1034	$221.10	$221.10	$221.10
Purchase #5	$20.74	8.711%	$22.5467	$22.55	$22.55	$22.50
Purchase #6	$189.40	8.408%	$205.3248	$205.32	$205.30	$205.30
Purchase #7	$211.67	9.277%	$231.3066	$231.31	$231.30	$231.30
7 purchase totals =	$1,146.01		$1,262.3105	$1,262.31	$1,262.30	$1,262.20