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	$102.42	9.672%	$112.3261	$112.33	$112.35	$112.30
Purchase #2	$157.43	6.535%	$167.7181	$167.72	$167.70	$167.70
Purchase #3	$157.81	13.379%	$178.9234	$178.92	$178.90	$178.90
Purchase #4	$13.94	9.646%	$15.2847	$15.28	$15.30	$15.30
Purchase #5	$240.66	6.331%	$255.8962	$255.90	$255.90	$255.90
Purchase #6	$179.50	13.587%	$203.8887	$203.89	$203.90	$203.90
Purchase #7	$51.76	10.819%	$57.3599	$57.36	$57.35	$57.40
7 purchase totals =	$903.52		$991.3971	$991.40	$991.40	$991.40