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	$37.52	13.654%	$42.643	$42.64	$42.65	$42.60
Purchase #2	$92.74	9.601%	$101.644	$101.64	$101.65	$101.60
Purchase #3	$205.90	7.597%	$221.5422	$221.54	$221.55	$221.50
Purchase #4	$100.72	9.509%	$110.2975	$110.30	$110.30	$110.30
Purchase #5	$192.69	10.807%	$213.514	$213.51	$213.50	$213.50
Purchase #6	$114.59	10.766%	$126.9268	$126.93	$126.95	$126.90
Purchase #7	$205.31	8.483%	$222.7264	$222.73	$222.75	$222.70
7 purchase totals =	$949.47		$1,039.2939	$1,039.29	$1,039.35	$1,039.10