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	$106.36	12.712%	$119.8805	$119.88	$119.90	$119.90
Purchase #2	$205.53	6.498%	$218.8853	$218.89	$218.90	$218.90
Purchase #3	$142.86	11.604%	$159.4375	$159.44	$159.45	$159.40
Purchase #4	$201.88	7.848%	$217.7235	$217.72	$217.70	$217.70
Purchase #5	$54.52	13.767%	$62.0258	$62.03	$62.05	$62.00
Purchase #6	$105.82	11.145%	$117.6136	$117.61	$117.60	$117.60
Purchase #7	$164.53	10.775%	$182.2581	$182.26	$182.25	$182.30
7 purchase totals =	$981.50		$1,077.8243	$1,077.83	$1,077.85	$1,077.80