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	$112.79	5.777%	$119.3059	$119.31	$119.30	$119.30
Purchase #2	$225.99	13.476%	$256.4444	$256.44	$256.45	$256.40
Purchase #3	$108.51	5.581%	$114.5659	$114.57	$114.55	$114.60
Purchase #4	$228.85	13.314%	$259.3191	$259.32	$259.30	$259.30
Purchase #5	$187.59	4.806%	$196.6056	$196.61	$196.60	$196.60
Purchase #6	$183.72	3.842%	$190.7785	$190.78	$190.80	$190.80
Purchase #7	$221.37	9.775%	$243.0089	$243.01	$243.00	$243.00
7 purchase totals =	$1,268.82		$1,380.0283	$1,380.04	$1,380.00	$1,380.00