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	$131.84	4.276%	$137.4775	$137.48	$137.50	$137.50
Purchase #2	$155.77	8.494%	$169.0011	$169.00	$169.00	$169.00
Purchase #3	$154.53	12.536%	$173.9019	$173.90	$173.90	$173.90
Purchase #4	$132.42	11.801%	$148.0469	$148.05	$148.05	$148.00
Purchase #5	$160.51	8.650%	$174.3941	$174.39	$174.40	$174.40
Purchase #6	$43.68	7.714%	$47.0495	$47.05	$47.05	$47.00
Purchase #7	$167.50	13.741%	$190.5162	$190.52	$190.50	$190.50
7 purchase totals =	$946.25		$1,040.3872	$1,040.39	$1,040.40	$1,040.30