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	$248.46	12.449%	$279.3908	$279.39	$279.40	$279.40
Purchase #2	$198.88	12.131%	$223.0061	$223.01	$223.00	$223.00
Purchase #3	$48.39	9.314%	$52.897	$52.90	$52.90	$52.90
Purchase #4	$65.81	6.528%	$70.1061	$70.11	$70.10	$70.10
Purchase #5	$136.96	3.127%	$141.2427	$141.24	$141.25	$141.20
Purchase #6	$120.39	11.225%	$133.9038	$133.90	$133.90	$133.90
Purchase #7	$187.37	9.581%	$205.3219	$205.32	$205.30	$205.30
7 purchase totals =	$1,006.26		$1,105.8684	$1,105.87	$1,105.85	$1,105.80